Manson Hot Air Engine - Free Plan

I got interested in hot air engines earlier this year and wound up building the popular Moriya model designed by Dr.  James Senft.  I got lots of help and encouragement from the guys on the Home Machinist forum.  There's a pretty lively discussion of the entire build here, including a link to a copy of Dr. Senft's original plans.

Sometime later I got interested in the Manson-style hot air engine, mostly due to its simplicity.  Surprisingly, I wasn't able to find a complete set of drawings for a Manson engine, so I tried to come up with an original design.  My first attempt was similar in a lot of ways to the Moriya engine, but it didn't run very well.  The next effort was kind of a cross between the partially complete plans found here and the build log for yet another example found here.  It ran much better than the first attempt, but still wasn't great.  But once again, the guys on the Home Machinist forum came through with some great hints for improvement, and with them, a third engine very similar to the second one ran like a champ.  There's even a video:

 

 

The Plans

This file contains a Fusion 360 model for the third version, 2D drawings based on that model, photos of most of the parts, and a few miscellaneous notes.  If you have any questions or comments about these plans, I'd love to hear them, either here or in a comment attached to the video mentioned above.

Trash to Treasure -- How to Make Stuff from Scrap HDPE

 Overview

Five or six years ago I ran across an article where some guy had melted down some empty plastic milk jugs and used the material to make the head for a mallet.  While I'm not exactly an environmentalist, the cheapskate in me was attracted to the idea of making something useful out of apparent trash, so I decided to try it myself.  I've been fooling with the process off and on since, and figure it's time to add what I've learned to the existing folklore.

On the surface it's all pretty simple.  You melt a bunch of plastic scraps together, maybe transfer the resulting blob into a mold, and let it cool.  There's a pretty good series of three YouTube videos that starts here where a gentleman named Randy Knapp shows how he does it, with what I consider to be exceptional results.

Material Selection

The first thing to figure out is what kind of plastic to use.  From what I can tell, the best candidate for doing all this at home is High Density Polyethylene, or HDPE.  You'll find plenty of it in your trash can.  It melts at a reasonably low temperature, and it won't give off a bunch of toxic fumes when heated.  You can easily identify HDPE by looking for a triangular recycling symbol with the number 2 in it.

Unfortunately, not all HDPE is the same.  When heated, some variants form into a rubbery sticky blob that has to be more or less forced into a particular shape.  Others become almost liquid so that they will settle by gravity alone to completely fill whatever container they're in.  The measure of this "runniness when heated" quality is called the melt flow index, or MFI.  Wikipedia has lots more to say about it here.  If you poke around on Dow Chemical's website, you'll find a huge variation in the MFI (and other parameters, too) among their HDPE products.

This brings up the question: Do you want material with a high or low MFI?  The answer depends on how you plan to cast the material into the shape you want.  One way, as shown in Randy's video, is to let it cool in the same container you melted it in.  In this case, a high MFI is better because the HDPE will flow nicely into the container.  Any bubbles will (eventually) rise to the top, and with luck the result will be a solid block of uniform material.  Although Randy clamps a board over the top of the material after it has started to cool, I haven't seen where this has much benefit when cooling in the same container that was used for melting.

As mentioned, HDPE with a lower MFI doesn't really melt.  Instead, it sort of softens into a rubbery, sticky blob.  You can deal with it, however, by manually kneading it and twisting it while hot (You'll need gloves for sure!) to force out the bubbles, perhaps several times as more and more material is added to the mix.  Then when enough material is ready, you can let it solidify in a mold with a lid that allows you to apply clamping pressure to force the blob into the mold.

You'll notice (and be disappointed) that the HDPE items in your trash can don't have the MFI printed on them along with the recycling symbol.  So, short of heating it up and seeing how it behaves, how do you tell what you've got?  Here are a couple of hints based on what I've observed:

1.  The two common ways to make HDPE parts are blow molding and injection molding.  There's a good description of the differences between them here.  In general, the MFI of blow molded items like milk jugs, bottles, and similar hollow, thin-walled containers will be lower than that of injection molded items.  You can expect, then, that milk jugs and bottles will soften into the "sticky rubbery blob" state, and that material that was originally injection molded will tend to settle by gravity into the container it's melted in.

2.  Among different samples of injection molded material, those with the highest MFI will be the most flexible for a given thickness.  I say this based on my own observations, along with the statement from the Wikipedia article mentioned earlier that "The plastics engineer should choose a material with a melt index high enough that the molten polymer can be easily formed into the article intended, but low enough that the mechanical strength of the final article will be sufficient for its use."

One last hint on material selection is to try to use as close to the same material as you can in any given batch.  It's tempting to just throw together bits and pieces of whatever's lying around, but if you try to mix material with different characteristics, you're much more likely to have problems with voids, cracks, and places where two different kinds of plastic don't fuse together properly.

Melting

When it's time to melt a batch of HDPE, about all you have to do to get it ready is to make sure it's clean, then cut it up into pieces that will fit in your melting container.  If you have a bunch of really odd-shaped items, it might be useful to shred them so they pack efficiently into your container.  But otherwise I don't think shredding has any benefit.

You'll want to melt your plastic in an oven at about 350 degrees F.  HDPE has very poor thermal conductivity, so if you're dealing with thick blocks of material, it will take a long time for them to heat throughout.  Avoid the temptation to speed the process by raising the oven temperature.  If the oven gets too hot, the plastic will burn and smoke and you'll get an icky brown layer on the surface of the material.

If you're using plastic with a high melt flow index, it will be easy to see when the material has become semi-liquid and started to flow into the pan.  But it's not so easy to tell when the bigger pieces have melted completely.  It's also not easy to tell when all the bubbles have risen to the top and popped.  For both of these reasons, it a good idea to let the batch cook for a good long while before you let it cool and solidify.

Mold Options

As shown in Randy's video, a non-stick brownie pan works well if you plan to cool the material in the same container you melt it in.  The non-stick surface and the sloped sides make it easy to remove the cooled plastic from the pan.

However if you want to use low-MFI material, you will need a mold that somehow allows you to clamp down on a lid to force the plastic into the mold under pressure.

I prefer the high-MFI, cool-in-the-melting-pan approach myself, but sometimes don't want to make a whole brownie pan full.  So I sort of went overboard and made this mold where you can move one side to make blocks of various sizes:

This thing just barely fits in my thrift shop toaster oven.  It doesn't have a non-stick coating or any draft to aid in removing the cast plastic, but since it comes apart, this isn't a problem.  Naturally, you have to plug up the unused holes to prevent the plastic from leaking out.  When I do find myself needing to compress some low-MFI material under pressure, I just cut a piece of plywood to match the current position of the moveable partition, and squish it down with C-clamps.

Working the Plastic

Once you have a nice block of HDPE, you'll be happy to discover that you can work it with most any of your woodworking or metalworking tools.  In particular, it's a lot of fun to machine on a mill or a metal lathe because you can remove material much faster than you would ever dream of with metal.

About the only thing that doesn't work is sandpaper.  HDPE is pretty resistant to abrasion, and when you try to sand it--especially by hand--nothing much happens.

My Projects

Here are some of the things I've made from recycled HDPE.

I made this extremely crude oscillating cylinder engine a few years back as an exercise to see what I could do with the material.  HDPE tends to be slippery (sort of like Teflon), so it worked well for the engine's simple bearings, piston action, and the seal between the wobbling cylinder and the stationary upright.  Unfortunately, over time the plastic parts warped enough that the ending bound up too tight to run.  (More on that under "Limitations" below.)

These trunnions for the tilting table on a disk sander are another place where HDPE's slipperiness made it easy to get a tight, low-friction fit between two parts.

HTPE is waterproof, so it worked well for these replacement axles, bushings, and wheels for a pool sweeper.

 

This replacement walker ski takes advantage of HDPE's abrasion resistance.  It and its mate have been in use for a couple of years and show almost no sign of wear.

Limitations

Obviously, you'll be limited in how big a piece of HDPE you can cast by the size of your oven.  What's less obvious is that it's difficult to make very thick pieces.  In my experiments, blocks more than about 1-1/2" thick almost always have internal voids in them.  These flaws are not round like bubbles would be, but appear more like tears.

This is pure speculation on my part, but here's what I think causes these voids.  HDPE shrinks a lot when it cools.  (That's a fact.) Before it has a chance to solidify, this shrinkage is relatively uniform throughout, and the block just gets smaller.  But since the block naturally cools from the outside in, eventually the top, sides, and bottom solidify to make a rigid shell that surrounds the still-molten material inside.  Then as that material tries to shrink within the rigid shell, something has to give and the inner material basically tears itself apart.

Even if these internal voids don't materialize, I believe that the cooling process creates internal stresses in the material.  These are what probably caused the warping over time of the parts in my little wobbler engine.  As it turns out, you can anneal the material to help mitigate this problem.  This website [] has more details on that process.

One last problem is that most adhesives won't stick to it at all. I've never had any luck trying to weld it, either. But bolts and nuts and screws all work, so it is possible to fabricate items with multiple parts if you don't mind using mechanical fasteners.

Greene and Greene Stereo Cabinet - Finished!

Greene and Greene Stereo Cabinet - The Top

I got lazy and neglected to take any construction photos while making the top. But no matter, really, since it's almost exactly like the one on the Aurora nightstand. Several of the posts in this blog series show how I made the nightstand top and its fancy ebony splines.

Greene and Green Stereo Cabinet - The Doors

The doors are made from the same plywood that I used for the sides and back of the cabinet.  I trimmed them all around with solid wood to hide the plywood edges, then just glued on the fake rails and stiles.  This picture shows one of them about halfway done.

I thought about using some fancy Brusso brass leaf hinges for this project, but the only ones I could find seemed a little big and a little pricey.  So instead made some the right size from some 1/8" aluminum plate for the leaves and some 1/4" aluminum rod for the pins.

I paid for a little bit of poor planning surrounding the hinges.  First of all, it was no fun at all cutting the hinge mortises in the part of the cabinet that I had already put together.  That would have been much easier if I had done it before assembling the front frame.  The other problem was the stupid decision to mount the hinges in a little way from the outside edge of the doors.  This made it somewhat challenging to actually hang the doors.

Normally you're supposed to 1) attach the assembled hinge to the cabinet, 2) slide the other leaf into the mortise on the door, and 3) install the screws into the door.  But I couldn't do step #2 the way I mounted the hinges.  So instead I had to screw the leaves to the cabinet and the door, then hold the door in place and then install the hinge pins.  That wasn't a show stopper by any means, but I did spend a few minutes wishing I had a third arm.

Greene and Greene Stereo Cabinet - The Drawers

The drawers in this cabinet are put together the same way as the drawer in Darrell Peart's Aurora Nightstand, with a big finger joint attaching the sides to the front, and a couple of ebony plugs for good measure.  As in the nightstand, they slide on wooden runners attached to the inside of the case.  These drawers are big enough that I probably should have used ball bearing slides instead of the wooden runners.  As it is, I'll have to be careful not to overload them.  Live and learn.

I made the drawer bottoms from solid poplar.  The bottoms float in grooves cut into the sides and the front, and are supported in the back by a little metal clip.  This arrangement allows them to expand and contract as the humidity changes without tearing themselves to bits.

Blocks at the back of each runner limit the travel when the drawers are shut, while some little tapered shims center the drawers from side to side when they are fully closed.

Greene and Greene Stereo Cabinet - The Back Panel and the Shelves

With the front and sides all put together, it's time to measure the as-built cabinet width and make the back and the two internal shelves to fit.

The back panel looks suspiciously like the side panels.  In fact, it's the same, except a little bit wider.  Like the side panels, it's just a piece of plywood with the faux rails glued on.  The shelves are even simpler; they're just rectangular chunks of plywood.

The two shelves and the back are all attached to the sides with screws that run through little wooden ears glued to the plywood panels.  This makes them easy to remove and replace as needed during construction and especially later when it's time to stain and varnish the remaining parts.

Greene and Greene Stereo Cabinet - First Assembly

On a project like this, it's really hard to get into all the corners and whatnot with sandpaper after it's put together.  So to make things easier, I installed the decorative ebony plugs in the legs and then pre-finished all the parts before gluing them together.  The finish is some water-based dye stain followed by multiple coats of wipe-on polyurethane.  I may or may not stain the inside later, depending on whether I have any stain left after doing the back, top, doors, and drawers.

Greene and Greene Stereo Cabinet - The Front Frame

The next big step is to build the assembly that includes the two front legs and the horizontal pieces that connect them together.  Then when that's done, I'll measure its as-built width and make the internal shelves and back panel to fit.

The front horizontal pieces all have tenons on the ends that fit into mortises cut into the front legs.  Because it's a lot easier to trim a tenon to fit an existing mortise than the other way around, it makes sense to work on the legs first.

 Each front leg has six mortises for the front horizontal pieces, five more for some decorative ebony plugs on the front face of the leg, and five round holes for the dowels that align it with the side panel.  The rear legs only have the dowel holes.

I tried a new trick to lay out the mortises.  Rather than marking their locations one at a time directly on the wood, I used a CAD program to make some little paper templates.  Each template has the outline of a mortise, along with its center line and a second reference line that represents the edge of the board.  After folding each template along that second line and hooking the fold over the edge of the board, it was easy to align the center line on the template with a mark on the board to precisely establish the mortise position.

Once all the mortises were cut, I was then able to make the horizontal pieces with their tenons to match.  I cut the tenons slightly oversize on the table saw and then trimmed them to fit with a chisel.

Here's a dry fit of the front assembly, before cutting the curved edge on the lower skirt:

Greene and Greene Stereo Cabinet - The Side Panels

With a design in hand, I hitched up my trailer for a trip to the lumber store.  Although Spellman Hardwoods is the biggest hardwood dealer in Phoenix, they've always been more than accommodating to me and my tiny (by their standards) little orders.  This time was no exception.  I came home with a stack of rough-cut African mahogany for the solid parts of the cabinet, and a sheet of mahogany veneer plywood for the side and rear panels.

Given the difficulty of storing and handling full sheets of plywood, I decided to chop the plywood into bite-sized chunks and work on the side panels first.  Each of them is just a piece of plywood with three faux rails glued on.  Instead of trying to cut the rails to exactly match the size of the panels, I took a page from my own playbook by making the panels and rails slightly oversize, gluing the rails to the panels, and then trimming each edge of the assembly with a single cut.

The legs will eventually be glued to the front and back edges of the side panels.  Here you can see one of the holes for a dowel that will help align one of the legs with the panel during assembly.  You can also see a little channel I cut into the back of the faux rail to keep glue from squeezing out onto the face of the panel.

The back panel is almost the same as the side panels, but I'll wait to make it until I can measure the as-built front of the cabinet to see exactly how wide the back panel should be.

Greene and Greene Stereo Cabinet - Genesis

For some time I've been wanting a dictionary stand of some sort to keep my big unabridged dictionary handy for occasional use.  At the same time, I've been needing to replace an old stereo cabinet that was originally built to store a bunch of vinyl LPs that have long since been replaced by CDs and digital music files.

My first thought was to combine the book stand and the stereo cabinet into a single unit, but I couldn't come up with a good way to integrate a tilting support for the dictionary with the rest of the cabinet.  So I decided to punt by making the stereo cabinet about the right height to support a separate book rack (to be built later) that will just sit on top.

Having built a copy of Darrel Peart's Aurora Nightstand and an almost-copy of his Rafter Tail Table, I wanted to make the stereo cabinet in the Greene and Greene style.  After way too much time fooling around with SketchUp, I settled on this:

 

The three drawers at the bottom are for CDs and miscellaneous junk.  The two doors at the top open to reveal the stereo itself: a CD player that sits on the shelf immediately above the topmost drawer, and a receiver that sits on its own shelf above the CD player.  The tray at the very top holds a laptop computer for playing digital audio files.  I'll normally operate the laptop remotely from a separate computer, but its tray slides out in case I need to access it directly.

You may grab a copy of the SketchUp file here if you're so inclined.

Rolling Stool - Free Plan

I always wanted one of those five-legged stools like the doctor scoots around on when he has you trapped in his little examination room.  So I built one, using some beetle kill pine from the rack at Home Depot and some swivel casters from Harbor Freight.  It looked like this:

I figured from the beginning that sitting on it would tend to pry the legs loose from the little hub-like piece near the bottom, so I was very careful to attach the legs firmly to the hub.  So far, so good.  So far, so good, that is, until one day the hub itself split in two as I sat down on the stool.  Oops.  Butt, meet floor!

Design attempt #2 worked out much better.  It looks like this:

With the legs transmitting the load directly from the seat to the wheels, it's not trying to rend itself asunder when you sit on it.  Better materials (hardwood and metal tubing) didn't hurt, either.

Free Plan

This PDF file contains detailed drawings for all of the stool's parts as I built them.  There's also a SketchUp model here.  I made all of the wooden parts from oak, and the metal parts from 1/2" thin-wall electrical conduit.  I glued up some 3/4" boards to get the required thickness for the wooden parts.  I also had to glue together a couple of pieces edgewise to get a board wide enough for the seat.

Here are some hints that might be useful if you want to make one of these for yourself:

The Metal Parts

The metal parts are all straight sections of 1/2" thin-wall electrical conduit, so just cut them to length according to the plans.  If you want to paint the conduit, now is a good time so the paint can dry while you make the wooden parts.

The Seat

After you've cut out the seat, you'll want to put a slight round-over on at least the top edge so it doesn't cut into your leg when you sit on the stool.  Also, you'll need to accurately mark the center of the bottom surface for reference later when installing the legs.

The Other Wooden Parts

The hub, the feet, and the connectors are all drilled to accept parts made from conduit.  These holes need to fit the conduit fairly closely.  Since you probably don't have a 0.705" drill in your toolbox, make one by carefully grinding down both sides of an old 3/4" spade bit until a test hole in a scrap of wood fits the conduit.  Aim for a snug fit.

After cutting out the hub and the feet, carefully lay out the locations of the holes, then use a V-block for support while drilling with the modified spade bit.  Be careful to stop when you reach the depth indicated on the plans.

For the connectors, lay out the holes as before, then use the connector drilling fixture shown in the plans to hold the connectors at the proper angle for drilling.

Assembly

Start by gluing five of the connectors to the five feet, as shown in the plans.  Each connector should be centered on the top surface of a foot, with the hole in the connector aligned with the middle hole in the foot.

Next, insert the five spokes into the hub, as shown here.  (Click on any of the images for a larger view.)  Make sure the spokes are fully seated within the holes in the hub, then drill pilot holes halfway through the bottom of the hub and into each spoke.  Install a 1" sheet metal screw into each hole to keep the spokes from twisting or coming out of the hub.

Now assemble the feet and braces together with the hub and spokes as shown.  This may be kind of tricky because it all has to happen at once.  Start by positioning the parts so that all the braces and spokes extend just a short distance into the holes in the feet.  Then work your way slowly around the assembly from one foot to another, gradually pushing the metal parts into the holes until they are all fully seated.

Next, turn the entire assembly upside down on a flat surface so that the feet are all in the same plane.  Check one more time to make sure the braces and spokes are all fully seated within the holes in the feet, and use clamps and/or weights as needed to force the connectors against the flat surface.  With everything in position, drill pilot holes and pin the spokes into the feet using sheet metal screws as before.  Important: Here, the heads of the screws must be sunk into the bottom surfaces of the feet so they don't interfere with the installation of the casters later.  You don't need to pin the braces.

In the next step, you will complete the assembly and glue the five remaining connectors to the bottom of the seat.  To make this easy, it's helpful to install some temporary guides on the seat to help position the connectors correctly.  Starting from the center point you marked earlier, draw five radial lines, 72 degrees apart, on the bottom of the seat, as shown here:

Next, draw five 3" x 1-1/2" rectangles to represent the footprints of the five connectors.  These rectangles should be centered on the five radial lines, and positioned 1/4" in from the edge of the seat.  Finally, use hot glue or small brads to temporarily attach small strips of wood along two edges of each rectangle, as shown.  The connectors will register against these strips in the next step.

Now insert the legs into the connectors on the feet and slip the remaining connectors onto the top ends of the legs as shown.  As always, make sure the metal parts are fully seated into their respective holes.  Apply glue to the seat and the connectors, align the connectors with the temporary guides, and clamp the connectors to the seat.  Once the clamps are in place, remove the temporary guides and wait for the glue to dry before removing the clamps.

Install some casters to the bottom of the feet, and you're done!

Drill Press Table Counterweight

My drill press features the "lift it up and down with your hand" method for adjusting the table height.  This got old after a while, especially with a vise or a heavy workpiece on the table, so I started looking for a way to add a counterweight to make the process easier.

The best setup I found on the internet had a cable running up from the back of the table, over a pulley at the top of the column and then down inside the column to the counterweight itself.  Unfortunately, I couldn't make this work on my drill press because the motor mount was in the way of the cable.  There was also no really good way to attach a cable to the back of the table.

I eventually figured the next best thing would be to have pulleys just below the drill press head with the counterweight riding outside of the column.  The pictures show how I did it.

The bracket that holds the pulleys is made of red oak, and clamps to the drill press column with some long bolts.  The axles for the pulleys are 1/4-20 bolts that I just screwed into threaded holes tapped into the oak.

I machined the pulleys themselves from high density polyethylene (HDPE) scraps that I melted in an oven and then cast into a block under pressure in a wooden mold.  (That's another story altogether--this YouTube video and the very first part of this one show how to do it.) The HDPE plastic is kind of slippery, so I didn't need any fancy bearings or anything to make the pulleys work for this project.

The counterweights are simple wooden boxes with sand in them.  I adjusted the amount of sand in the boxes until the weight seemed about right.  In the end I think the whole assembly wound up about three pounds lighter than the table.

Small Parts Storage Trays

 

Here’s yet another way to store nuts and bolts and screws and whatnot. These trays are made from scraps of 1/4” MDF and 1/8” tempered hardboard left over from other projects.

I sized them so they will sit up on edge in a couple of the drawers in my work bench. That makes it easy to remove any one by itself while still utilizing most of the space within each drawer. For that to work, though, the sliding lids have to fit nicely against the dividers so the hardware doesn’t get all mixed up when the tray isn’t sitting flat.

You could also store them like books on a shelf.

To keep track of which tray contains what, I made an Excel spreadsheet on my computer that lists the contents of each tray. I keep a printed copy in the drawer with the trays so I can find the correct tray pretty quickly when I want to deposit or withdraw some random bit of treasure.

Biesmeyer-Style Bandsaw Fence - Free Plan

I have a Taiwanese clone of the Delta 14" bandsaw that I bought used without a fence.  That didn't bother me too much at first, because I thought that I would be using it to cut curves most of the time, and that when I did need a fence, I could just clamp a board to the table.  But then I found out how useful a bandsaw is as a ripping machine and for certain kinds of joinery, and how tedious it is to accommodate drift using the clamp-a-board-to-the-table method.

I needed a real fence.

I thought about building the shop made fence described by Patrick Sullivan in Fine Woodworking #210.  But when I looked at it closely, the design seemed overly complicated to me.  So I set out to build something simpler that would still get the job done.  After a couple of false starts, I eventually came up with the Biesemeyer-style fence described here.

I started with a piece of 1-1/4" x 1-1/4" x 1/8" 6063-T5 aluminum channel for the rail.  I cut one leg off at 13/16" as shown in this drawing.  I then drilled it to match the mounting holes on my bandsaw table and cut a little notch to match the bandsaw's miter slot.

Then I made the "slider" shown in this drawing.  It rides to the left and right along the rail and clamps in place with a little bolt.  The longish piece on the bottom of the slider registers against the rail to align the slider, while the shorter piece carries a T-nut for the bolt that clamps the slider to the rail.  You could use a threaded insert instead of the T-nut if you want.  If you look carefully, you'll see a little piece of bent sheet metal that prevents the slider from marring the aluminum rail when you crank down on the bolt.  I called this thing the "rail protector", and it's shown in this drawing.

There are also two T-nuts in the holes on top of the slider.  These receive a couple of bolts that hold the base of the fence to the slider.

This drawing shows the base of the fence itself.  It's cut out on the left side to clear the bandsaw's yoke when the fence is positioned towards the left side of the bandsaw table.  The hole and the curved slot nearest the operator accommodate bolts that attach the base to the slider.  The curved slot allows the base to rotate in order to adjust for drift.

The other holes in the base have threaded inserts or T-nuts that allow attachment of the auxiliary high fence shown in this drawing.  It can be installed in either of two orientations for resawing or to accommodate various workpiece thicknesses.

You might want to use star knobs instead of the bolts that I have shown for the clamp bolt in the slider and the bolts that attach the base to the slider.  You might also might want to make the slider and base out of aluminum instead of wood!