Hello all

Think you have trouble misplacing you full size chuck key? How would you contend with this size(I have misplaced it several times myself whilst making it!!)

Sorry about the orientation.

It’s a 1/3rd scale miniature 80mm 3 jaw chuck. It still needs finishing off, the pinions are my next stumbling block really. If there is interest I can explain how I made certain parts!

Thanks for reading

William

Hello all

Thank you for the kind words, its just going to stay a standard chuck, as I am not an owner of an 80mm Griptru!

I have done one pinion, Its not right as I forgot about the involute detail when grinding the D bit!:

As can be sen here the middle D bit just has straight sides, I am yet to experiment with making a involute form D bit so watch this space. I am using a D bit as I don't think any other cutter would work. A fly cutter style tool or a commercial cutter as it has to clear the pin sticking out the front of the pinion.

That's the pinion before I cut the teeth,

Okay you asked for an explanation on the finer details so here goes:

The scroll and jaws have so far turned 2 of these 0.5mm slot drills

To;

The scroll and jaws are machined on my Alexander 2c pantograph engraver using the full size original, and the pantograph ratio set to 3:1. I first roughed out the ends of the jaws using a 1mm endmill and a 3mm stylus, (the pantograph ratio x cutter dia = stylus dia) Then I moved on to the 0.5mm slot drill and a 1.5mm stylus to finish machine the profiles.

Getting set up here is the most difficult part one has to really be creative with an indicator!, I needed to get the "fence"(1,2,3 block) on the copy table in relation to the fixed jaw on the vice on the machine table. This was done by calculating the centre of the original jaws plus the radius of the stylus, turned out to be 4mm exactly. A slip gauge was used. Then holding the stylus against said "fence" and slip and sweeping an indicator either side of the 1/3rd scale jaw on the machine table to centralise it.

The 0.5mm slot drill is running at full lick of 20,000rpm, 0.1mm depth of cut set with the knee on the machine, about 30mins per jaw

The scroll was largely the same process, only I used the 0.5mm cutter to fully machine it, no roughing cuts. I removed the copy table and held the original scroll on a mount. Sorry no pictures of this stage! so you will just have to put up with my explanations. The scroll took about an hour and a half to machine.

The jaws were made out of a strip of gauge plate which I surface ground in my lunch break at work to fit the slot in the chuck body, the slots either side were cut using a little T slot cutter, in this set up, enables both sides to be at exactly the same depth etc.

The T slots in the chuck body were cut in this little fixture on the BCA ,slot first then using a miniature carbide "key seat" cutter (off ebay, Klot carbide, no links just an impressed customer). the fixture allowed easy lineing up with the pre drilled pinion holes that were drilled when it was still attached to the parent stock from turning the i.d. and o.d etc

The gears were cut on the Pantograph using the aforementioned D bit in this set up:

I hope that explains a bit!

William

Edited By William S on 01/04/2021 23:28:09