Category: Model Engineering

Change Wheel Calculator for Warco 918 Lathe

Posted on by Adam

Here is a spreadsheet to calculate all the thread pitches possible on a Warco 918 lathe using the change wheel set provided with the machine :  XLSX (newer versions of Excel) and XLS (Excel 97 and 2003, also works in LibreOffice/OpenOffice).

The cells are all locked except D4, which should be set to “y” or “n” depending on whether the 120/127 tooth gearing will be in use (see the plate attached to the lathe). Note that there are three worksheets for mm/rev, inch/rev and tpi.

Use should be self-evident, but in case not, here is an example.

Looking at the “mm per rev” sheet:

  • Put “y” in cell D4 because that gives results in nice round numbers
  • Assume you want 1.5 mm/rev
  • See this appears in four cells: I13, I14, F19 and C24
  • Choose F16 (on a whim, or maybe you already had a 36 tooth wheel in position b)
  • Change-wheels (where a and b are as on the plate attached to the lathe) to use are: a=45 tooth and b=36 tooth
  • The gearbox should be set to no. 4
  • Note that the Warco lathe-plate gives the C24 configuration.

If unsure, check you understand it by choosing a few of the pitches given on the lathe-plate and confirming that the change-wheels and gearbox settings you determine from the spreadsheet match the “right answer”.

Warning: I might have made a mistake so always try out on a piece of scrap and measure the result.

 

Making a Trepanning Tool – Notes and Plans

Posted on by Adam

I’m planning on cutting some gear wheels and, having struggled with using a hole-saw to cut blanks, decided a trepanning tool was probably the answer.

The tool is only meant for cutting 1/8″ thick stock. Tested on brass and aluminium (may not be up to the job with steel). Use low speeds and if you don’t know what you are doing, don’t do it!

The Finished Trepanning Tool

The dark colour of the main body is due to a (failed) attempt to case harden the pilot; it is just uncleaned scale from from heating. I actually found the setup to be sufficiently rigid that the pilot didn’t take any load with 1/8″ brass and the narrow cutting tool shown below in the bottom right of the picture.

 

Trepanning Tool (click for larger size)
Trepanning Tool (click for larger size)

The Plans

These are not proper dimensioned drawings in an engineering sense, and were produced as part of the design process, but they should be sufficient. Stock used was steel 1″ dia bar and 3/8″ square.

Trepanning Tool Assembly (click to open full-size image)
Trepanning Tool Assembly (click to open full-size image)

Also available as a DXF File.

Brief Construction Notes

Arbor

Cut 1″ dia stock to slightly over length

3 jaw chuck :-

  • face off (light cuts), centre drill and support with tailstock centre
  • turn down 1/2″ shank
  • brighten up about 1/4″ of 1″ dia body (used later for concentricity setting with DTI)
  • cross-drill, widening progressively to 7/16″ (ideally finish to size with reamer)
  • drill and tap M5 (and shorten M5 cap screw to match)

4-jaw chuck :-

  • hold using 1/2″ shank, adjust to near zero runout with DTI
  • turn pilot (should be concentric with shank)

Cutter Arm

3/8″ square stock

4-jaw chuck :-

  • face off both ends (low overhang from chuck)
  • centre-drill second end, loosen 2 adjacent jaws, withdraw from chuck and support on centre, retightening the jaws to same setting
  • turn to 7/16″ dia to fit arbor

Pillar drill :-

  • drill and ream 3/16″ for cutting tool
  • drill 1/8″ for end of slot
  • drill for clamp bolt (M4 tapping drill size)
  • cut 1/32″ slot
  • drill clear for clamp bolt (up to slot)
  • thread M4 for clamp bolt

The Cutting Tool

Grind a 3/32″ or 1/16″ wide cutting point. Give it plenty of side clearance because the tool will be making an arc. Tighter arcs => more side clearance will be needed at the expense of a weaker tool.

Since round tool steel is used, the cutter can be rotated to adjust the in-use clearance a little to compensate for slightly uneven grinding, and changes in cutting radius, but I suppose the cutting face should be fairly close to lying on a radial line.

Model Engineers Depth Gauge

Posted on by Adam

Having recently faced some cylinder drilling, I finally got around to making a depth gauge. It took about a morning. The sizing is very-much determined by available parts, starting from the springs and having some 3/8″ OD brass tube with nice thick walls (ID approx 1/4″) to hand. Two springs gave me about the 1 1/2″ of gauge travel I wanted.

No dimensioned drawings this time, but see below for a photograph of the disassembled gauge from which you should be able to work it out. In lieu of drawings, here are a few notes…

  1. The end cap was made first, drilled to about 1/64″ less than the OD of the brass tube. You can see where I then turned down the tube to get a nice press fit. I’m very fond of press fits: most satisfying and clean. If you over-do it then you can always braze/solder but it never looks so nice. I have a small arbor press.
  2. The other end of the tube was threaded using ME 3/8″ x 32 TPI since this matches the tube OD and is a fairly fine thread.
  3. The 1/4″ spring-stopper on the 1/16″ central “spike” was another press fit thanks to some metal forming as I parted it off. Don’t bend the spike!
  4. The thumb screw was made by tapping (5BA) a shaped and parted-off piece of hex stock, screwing a 5BA cheese-head screw firmly into place with a bit of thread-lock and then turning away most of the head. NB: face, chamfer, drill, tap, insert screw and turn-off head are all done without removing the work from the chuck.

The images above are links to larger photographs.

 

Liking LibreCAD – Free cross-platform 2D CAD

Posted on by Adam

I’d been using DraftIT for a number of years when I wanted to be able to work on plans using both my home computer (Win XP) and work laptop (Ubuntu Linux) while the family uses the home PC. After some searching, I came across what is now called LibreCAD. It takes a little while to adjust (I suppose this is always the case) but I must say “it works for me”. It isn’t too hard to pick it up by trying and it is possible to do simple stuff without having to understand everything it does.

Best of all, it saves as DXF format, while this only comes with the “Pro” version of DraftIt which costs £99.  DXF is a de-facto standard so this makes the drawings more sharable and – maybe more important – gives me more confidence in being able to read/alter drawings for longer (e.g. if the makers of DraftIT vanish).

Recommended!

Making Elmer’s “Tall Vertical Open Column”

Posted on by Adam

The late Elmer Verburg designed quite a few relatively-easy-to-build model engines. All are made from bar stock. The second one I have made is #32, the “Tall Vertical Open Column”. As many people do, I made a number of minor changes. These are described here, along with some construction notes I wrote to help myself, some observations and some pictures.

The plans can be found online in several places: there are several “Yahoo Groups” as well as “jon-tom.com“. I have also uploaded them (see “Files” section).

Notes and Comments

I opted not to paint the base and top platform, having previously made a mess of painting. Instead, I left them relatively “raw”: the as-rolled large faces of the bar stock were very lightly cleaned up and the edges were draw-filed. I’m fairly happy with this approach and like the contrast with the shiny flywheel and brass components.

In the interest of simplifying construction – and reducing the need for careful working, which is not my strong point – an alternative method of constructing the eccentric sheave and the arms that ensure a straight-line motion of the piston rod were used. See the “Files” section below.

The only problem encountered on assembly was that the straight-line that the arms followed did not match the piston rod. It is worth making the holes on the base plate of the cylinder assembly a bit slack to allow for adjustment but I ended up having to insert a 15 thou shim under one corner to get the motion to be “good and free”. I suspect that this is due to having used quite small AF hexagon rod for the columns such that it didn’t pull itself square on tightening. On the other hand, it could simply be a misplaced hole.

Quite a few of the joints leak slightly – see the video – since I just left them as metal-on-metal.

Some other examples on the web:

Files

 

Making Dice in Brass (or other metal)

Posted on by Adam

Here are some notes on making dice (or just one die) in brass (etc) in the metalwork shop, suitable for a total beginner. I did it with my 10-year old. I used some half-inch square brass stock.

  1. Set the stock in the lathe using a 4 jaw chuck. Get it close to centred by sighting the edges against the cutting tool. I tend to face off with a TCMT (carbide tipped) tool where the tip points away from the tool post (i.e. a 60 degree angle to the work). I used my top speed of 1800RPM but you could go faster.
  2. Face it off.
  3. Mark out and cut off slightly over 1/2″ from the stock, file it down a bit to remove the unevenness.
  4. Fly-cut (1″ or slightly larger fly cutter) the sawn face to get to a cube.  Use a speed of about 1100 RPM and work in stages of measure-then-cut. This is quite easy even in a small mill/drill. Lock the table in position and the head in place while cutting. A digital scale on the vertical axis is really useful for this (the vertical fine-feed on my machine is hopeless) . An alternative is just to face-off this end in the lathe but I find it easier to finish off at the correct length flycutting and it demonstrated the technique.
  5. Gently remove rough or sharp edges with a fine file or emery paper.
  6. Set up an arrangement like the photo. The tool clamp provides a positive location so that the die can be turned over and around and returned to the same position.
  7. Turn the cube over so that the previously-turned face is upper-most. Fit a centre-drill into the chuck with a point of the size you want the die dots to be. Traverse the milling table so that the centre of the face is lined up. The marks from the facing-off operation should be sufficient and give a nice appearance. (this is why you need to get it “close to centred” in step 1). Make sure  you remember to take account of backlash in the leadscrews. I made sure I approached the centre by turning the handwheels in a clockwise direction. Zero the collars or mark off the handwheel positions carefully.
  8. Drill to depth. Set the depth-stop and drill again to meet the stop.
  9. Remove the die, rotate to another face, snug-it up against the tool clamp and secure the die. Drill another centre hole (say for the “3” side) then a final hole (say for the “5” side). Remember opposite sides of dice add up to seven.
  10. Decide where the corner dots will be and traverse both axes of the milling table to position the cube appropriately. Traverse the same distance for each axis. I opted for a whole number of revolutions of the handwheels for simplicity. Remember to turn them the same way as in step 7 to mitigate for backlash.
  11. Reclamp the table and drill a dot. Loosen the milling vice and rotate the die by quarter of a turn. Repeat until you’ve made the “5”. Use the same process to make the “3”.
  12. It should now be obvious how to make the “2” and “4”. The “6” is made by making a “4” then return one of the milling tables to its “zero” position (step 7). Reverse back past “zero” by about half a turn of the handwheel them advance back to “zero”. Clamp the table and drill. Rotate half a turn and complete the last hole.
  13. Polish it up, slightly round off the edges and corners and you are done.

My daughter was well pleased with the result and rather impressed by the simple little tricks that make it quite easy to get a neat and regular result with minimal fuss and fiddle: the trick with the tool clamp, rotating the die, the depth stop. If I were to make another, I think I would place the “spots” slightly further from the edges.

Wallace & Gromit Inspired Arms in Brass/Steel

Posted on by Adam

Here is the product of a fancy, something less demanding than making something that really works. It was made relatively quickly from a page of sketches I made over a cup of coffee so it isn’t perfect. I’d probably change some details if I made another.

I’ve written some construction notes and transcribed my pencil sketches to a CAD drawing in case anyone finds that useful. I’d be pleased to hear of any improvements anyone makes.

Download: Zip of plans, construction notes and larger pictures (770kB total).The CAD plans were made using Draft-IT (by CADLogic) but a lower res GIF is included in the zip)

Cheers!

Model Watt Governor – CAD Plans and Construction Notes

Posted on by Adam

Having had a hankering to make a Watt-style governor but having failed to find any plans to my taste, I decided to design my own. Here it is, with 2D CAD plans produced with Draft-IT (and GIF images of the same) and my construction notes for download. The design is hand-cranked and lacking a valve lever because it was made as a retirement/60th birthday gift and I ran out of time to complete the valve lever (I wanted to assemble the governor before dimensioning the lever).

Inspiration for the design, and especially the proportions, came from Muncaster’s book and photographs I took of real governors.

All of the downloads are covered by the same Creative Commons licence as everything else on this blog. Feel free to adapt but I’d like to hear about modifications, ideas etc…

Downloads:

Orrery and Gear Spreadsheets from Mike Shuter

Posted on by Adam

Thanks to Mike Shuter, who commented on the previous entry, for sending me his two spreadsheets with Orrery gear ratios and the “continuous fractions” method of determining wheel/pinion pairs. He has permitted me to post them here but please contact “m [dot] shuter [at] ntlworld [dot] com” if you find them useful. Please do not repost without contacting Mike as he is the creator.

Mike Shuter’s Spreadsheets

Windows Program for Compound Gear and Orrery Calculations

Posted on by Adam

This is a first public release of a Windows program for calculating compound gears (2 pair of gears) in “normal” or epicyclic arrangement. It also fully or partially automates Orrery calculations and has presets for various solar system periods, which can be modified and added to by editing the PeriodData.xml file. It allows the tolerance and min/max gear sizes to be specified as well as having various customisable presets, e.g. to only use Meccano or Lego gear sizes.

It is not fully tested and must not be distributed in its present form; it may only be downloaded from here. When it is a little more improved I will post source code and intend to permit distribution eventually. i.e. I’m only granting you a licence to use it yourself at present; a liberal Open Source licence will happen eventually.

It is written in C# and anyone interested in working on the code should contact me.

Download: Compound Gear Calculator Installer (Windows MSI, 380Kb)

If you use it, please provide feedback.