Starting a Trent Pinion mill...

Hi,

I'm starting on my project to build the trent pinion mill kit sold by Hemingway Kits

Having looked at the drawings, i've tallied up the tools that i dont currently have that i will need in future, I'm of younger stock so i was brought up with the metric system and thus virtually all my tools, drills, end mills, reamers, slitting saws, etc.. they're all metric and nearly everything but the threads (thank god) are imperial.

I looked at how much it would cost me to buy all these reamers and drills and decided that it costed far too much so i'll try to improvise as i go along on some of the hole sizes, i've only bought what is totally necessary so thats 1mm number stamps and a 1" x 60 degree dovetail cutter. The lathe tools i can grind up.

I've never done proper stamping before, i was taught to just do it by rough guides and hand, but theres a 1" brass thumb nut that needs graduated lines and numbers stamped on it, i've got a dividing head with a chuck, of the milling kind but no facility in which to accurately cut the lines and press the numbers.

Has anyone out there ever thought of a home built jig or staking tool, that would conquer this challenge?

Michael W

I have seen plans around for making a dial engraver. My Brother in law has just completed one, he made his own pattern for part of it to be cast rather than fabricate it from solid. He lives in France so the casting was done here in UK.

Lines are cut with a sharp lathe tool like a screwcutting tool on its side or a bar holding a smaller tool. Then set up a changewheel or some such for indexing the lathe spindle while marking the lines by racking the tool using the saddle on the just turned handwheel. I think Hemingway do a kit for marking too.

There have been loads of stamp aligning tools and jigs in the magazines over the years, and on the net now. Just needs a bit of searching round build logs and reports on making clocks and tools that need dials.

Sounds like you need to visit Hemingway kits, check out graduating tools and universal pillar tool, both of which are hobby classics.

Mike

I dont really have the time to make a detent system for my lathe and i'm wondering if i can transfer the top slide over to the mill and line it up with the rotary chuck and cut so..two things i can see going wrong as such, the depth of cut is hard to determine and would have to be done with a rule and carefully moving the tool in the post and back lash from the feed screw of the top slide it isnt ideal but it seems like the only option ive got i'll grind up a sharp 40 degree inclusive tool to score them in.

As for the numbers, well it doesnt seem likely that i'll be able to do them at the same time but i could drill a 1 inch hole into a piece of metal and put a hole roughly the same size as the punch cross drilled into the 1 inch bore at that would give me a kind of "punching-collar-guide tool" that would ensure that atleast the number would always be struck true horizontally but ill have to hold it steady vertically some how, and ill have to work out the spacing between each number because i cant see what i'm doing whilst im hitting it.

This is the best and most convenient solution i can think of because specialist staking tools and engraving graduation tools cost alot of money, this is surely an exercise where the intuition of the maker must come into its own.

Michael W

An effective method is to use a fixed guide and calculate the angle offset from the true line position for each digit on multiple digit numbers. For example, the first digit on a two digit number might be done a little short of the line position and the second one a bit past it. My number stamps have square shanks so I cut a matching slot in a suitable piece of scrap and fitted a cap with two small screws to get a snug but sliding fit. My stamps have pretty smooth sides so it worked was as is. Some are rather rough forged and may need smoothing out with abrasive. Maybe have to operate a bit more so they are all the same size with numbers adequately central. Some of the economy ones aren't well lined up with the centre of the shank. Seems a lot of effort for first job but when its done its done and subsequent work goes fast. Don't loose the guide!

Worked well for me when I did the numbering for an "angle collar" to cover the renmants of the numbers on my Pratt & Whitney top slide which was quite damaged in that area. Hardest part of the job was calibrating the hammer blow to give even depths as the amount of hit needed varies with how complicated the number is. Never really got the 1 right! Found it best to do the job by strangling a club hammer, holding it close to the head so most off the effort came from the hammers own weight falling. More of punch than a hit I guess. Trying to calibrate a normal hammer swing for reliable results proved beyond me.

Clive.

I just use a bar held in the toolpost with a slot made to fit the punches in it as a guide.

A drop of micrometer blue can be used to check where the digit will appear.

A dead blow hammer would help avoid double registers.

Thanks for the response, Clive,

I think were both along the same line of thinking for the punch collar, my numbers have square shanks too so i'll have to drill a round hole thats nearly the same size as the width of the tool, i like the idea of the holding screws to improve the fit and will now include this, thanks. I'll do my best not to drop it into a pit of swarf !

I have the 1mm punches on order and although i havent seen them yet, judging by the quality of my 5mm ones they arent of the finest manufacture i presume and will expect some defect in alignment which is almost unavoidable.

I, like you, find that the shape of the number largely dictates the force required to press it appropriately, i will heed your advice. I do have a small arbor press and find if you can line it up correctly just pulling all your weight on that gives you some relatively even stamping, and you can even re-stamp old numbers if youre careful with it. maybe an idea for some that dont quite make the depth!

Michael W

Ah yes, Neil, i did think of that idea myself, using a lathe tool post attachment, but unfortunately for now i dont have any dividing facility on my lathe.

Michael W

Michael W

As mentioned by Michael Poole:

The definitive source of good engineering advice in this field would be Geo. H Thomas ... His books 'Dividing and Graduating' and 'Building the Universal Pillar Tool' were effectively a compilation of his 'Model Engineer' articles on the same themes.

The punch-holder is a sensible design, very well explained.

MichaelG.