Rotary Broach Tool Design

[excalibus]

That's an interesting idea Graham...

My lathe arrived last weekend, I have cleaned it down and made sure it all works etc and lubed it up...

The machine is a Sieg C2 lathe... I am now waiting on a couple of items before I begin to machine with it... Namely a machinist level to set up the bed and a precision test bar coming from interstate to use to check runout of the chuch and also to setup the tailstock to centreline... and of course the DTI is on its way already but the other 2 items will have to wait a week or two for the funds for them... Damn those machinists levels are not cheap ;D

So this idea of yours Graham would bolt onto the toolpost.... My saddle (I think thats the name of it lol) has a an angle degree gauge on it with markings from 45 to -45 degrees spaced every 2 degrees from 0 with the outer ends having an extra line for the last degree to 45... would this be accurate enough do you think for setting the cross slide to 1 degree.. eg setting the angle by eye to halfway between zero mark and the first mark on gauge?

I guess I will need a protractor to confirm the accuracy of the angle gauge...

 

[GRAYHIL]

You can use a clock guage to measure the angle of the holder/topslide.
Dead striaght = 0.000 reading on DTI over a set longtitudinal traverse
For angles take the tangent of the angle and multiply it by the distance traversed.
IE FOR 1DEG OVER 3" TRAVERSE
TAN 1*3
.0175*3
ANSWER .0525 DTI
See Kens DIAGRAM below in an earlier article
Graham

 

[GRAYHIL]

Heres mine
graham

 

[GRAYHIL]

more

 

[GRAYHIL]

and more

 

[GRAYHIL]

last one

 

[Ken I]

Well done Graham - as improbable as it seems it does work.

Regards,
Ken

 

[polygon]

I agree, nice work, and the pics are wonderful.

 

[rdhem2]

Thank you guys. You hit the nail on the head for what I need. Good straight information is never out of date.

 

[peterl95124]

I like this thread, very informative, since my mini-lathe only has an MT-2 tailstock and all the commercially made rotary broaches seem to be MT-3 or 3/4" shank, am considering a re-scaling of this design for MT-2, probably a fools errand, but I'm also only hoping to make pretty small broaches (first one only 1/8" hex). wish me luck, I'll probably need it. I think my biggest concern is the actual broaching tool bit itself, would prefer a commercially made tool bit, but a re-scaling of the holder means something less than 1/2" diameter tool bits.

 

[peterl95124]

don't know if Ken I is still reading his thread, I do have a couple questions,

about the bearings, up front there's just the thrust bearing, are that thrust bearing's grooves deep enough that they keep the tool bit holder centered, IE there's no need for a radial bearing at both ends of the holder, just one at the rear, seems a bit odd to me, so maybe its important to use a heavy duty (deeper grooves) rather than light duty (shallower grooves) thrust bearing ?

also the big end of the tool holder seems to fit into a bore in the bearing housing, how close a fit is that, what clearance, is it tight to keep the holder centered, or loose because it doesn't need to be tight and any rubbing would cause drag and "cause the broach to make a helix" as I think you've already pointed out IIUC ?