A Short Diversion to CNC

I am presently blocked on the Glass 2 Cylinder project while I decide what grinder tool rest I am going to build. Boring the cylinder head, which is brass, is showing me that my hand grinding of cutting tools is not adequate. This requires a trip to a metal supplier and so need to fill up the hobby cash pile first.

In the meantime,  I decided to revisit my previous CNC efforts. For the Unimat I used Mach3 (free edition) on a dedicated small PC. This worked well enough but it seemed overkill plus the learning curve for Mach3 is steep. After a bunch of browsing I came across Grbl and SmoothieBoard. SmoothieBoard requires a processor that I don’t have (it is partly based on Grbl though). For Grbl I only need an Arduino Uno, which I already have. It took some investigating to see if the 2.5D milling/routing that we want to do is supported by the limited G Code subset of Grbl. There are enough free tools to generate the code we need. Even helical threading is possible! 2014-07-16 16.28.19

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Pistons

Now that I have 2 cylinders, it is time to make the pistons. These are supposed be graphite, which is easily obtained. But that only works if the cylinders are perfectly round inside. And regular borosilicate glass isn’t perfectly round. Close but not close enough. Option B is to make pistons out of brass and add a groove for an o-ring.

I’m a big fan of Plan B anything. First up, cut some hex brass to just over the final length of 2 pistons plus room for finishing the ends and the .05 wide cutoff blade. My 4×6 band-saw takes no time at all. Some time spent aligning its blade means that cuts are close to perpendicular. Less post processing that way. At same time I also cut the cylinder block. It amazes me sometimes just how much scrap material my dad collected from various places he worked. The waste was incredible. After 40 years I am still using the scrap leftovers.

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Started: the Jan Ridders Glass Cylinder 4 Stroke Engine

After a month or so of building more add-ons for the Taig lathe and going over the drawings that Jan provided, the build has begun.

Jan Ridders designs and builds fascinating engines. Stirling, gas, steam, doesn’t matter. His designs are imaginative and buildable. Drawings are free for the asking, as is advice on building and further modifying them. The specific engine I am building has glass cylinders. This provides a lovely view of the engine firing. (The whole site is available in Dutch and English so you don’t need my ‘I speak Dutch’ super power.)RiddersGlassCylinderMk2

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Spinning around

Really, really almost done for now with my ‘must make’ tool list. My DW wanted to avoid looking at dark brass marks on my fingers at dinner. Since I will be turning knobs a lot while making my engine, it was time to retire the original brass handles on the carriage, cross slide and vertical milling slide. The handle design came from Keith Brooke’s excellent article on making zero-resettable dials for the Taig.

Making 1 of something is a simple task, making 3 identical units is something else. I marked out the dimensions on the first spindle, and then used that as a pattern for the other 3. Each was almost complete before moving on to the next one. The cross slide DRO was most useful. Touch the cutting tool to the material, zero the DRO, calculate diff between original and target diameter, divide diff by 2 and you get the desired reading for the DRO. (It always measures radius, not diameter). Wind the cross slide to the desired number, press zero again and now all you need to do is cut until you get to zero!

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Boring Head Arbor

Nearing the end of the Must-Do list prior to starting the Jan Ridders engine.

Several years ago I bought a lovely 30mm boring head from Chronos in the UK. I had adapted it to the Unimat and kept it after that lathe was sold. For the engine I need to counter bore various holes to seat bearings, a perfect job for the boring head.

Lee Valley supplied the blank arbor, I bought 3 this time and milled the tightening flats on all 3 to save that setup when I need to make a custom tool.

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A bit of turning, tapping with the die holder, polish up with emery cloth and oil to end up with a shiny new arbor. The thread is M10x1.5 .

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The overhang is as short as I can make it. The 6mm boring bars will need to be razor sharp and small feeds to avoid flexing them. A test cut prior to making the arbor worked quite well. More practice aligning the cutting edge should result in excellent bores.

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