Group Project: Rotary Broach-- Building complete, all shipped out!

No idea how much I would use it, but it would be fun and nice to have around. I'll join in.
 
Ah, I actually figured out the purpose of those 10-32 screws on the original drawing! When you are setting up a rotary broach, you need to make sure that the 'tip' of the tool when rotated has no runout. The 1 degree angle has to be offset in some way by the tool bit being held off center the correct amount to get it back to running 'true' at the tip.

This is what the funny-business about the "Broach is switched with a dowel pin of the same length when shank is on a Vee Block tip of pin is adjusted to not wobble" bit in the upper-right of the drawing!

In the drawing in my original post, I now can "see" that the body has some sort of side-to-side offset built into it, but I don't really see it listed as a dimension. it is MAYBE captured in the 'flange view' in the top-left of the drawing, where the mount holes are 200 thou off center, but I figured that was because it was a weird-3-view.

I'm guessing there is some math I need to do when designing this. I really like the idea of including a thrust and axial bearing if possible, but I've personally not seen any I am a huge fan of yet. I originally really liked the version in the OP because of how small the body is, but I guess that isn't particularly possible with an axial bearing.

Also, I see ttabbal's post, I'll add you to the OP!
 
If you have room, I'd like to play, too. I'm pretty good with a lathe, my PM25 mill is OK, but my 4" rotary table isn't the best for profiling.
 
T Bredehoft said:
If you have room, I'd like to play, too. I'm pretty good with a lathe, my PM25 mill is OK, but my 4" rotary table isn't the best for profiling.
Click to expand...
Great! I'll count you in!

I think we're going to end up doing a decent amount of changes to the design. I think getting us onto an axial and thrust bearing is a good idea. I found some needle-bearings, how do we feel about using some inexpensive needle bearings? Are there any downsides we should be aware of for those?

Next, I like the idea of a 'round flange' instead of the 2 bolt flange on the original design. I suspect that many of us are going to have trouble getting that sort of profiling done accurately enough.

For bearings, does anyone think needle bearings are a bad idea? I found this set (and some others of the same size) that could be pretty cheap: https://www.amazon.com/dp/B082PCTQ2...aWNrUmVkaXJlY3QmZG9Ob3RMb2dDbGljaz10cnVl&th=1

I THINK it means the 'broach holder' would have to be pretty accurately manufactured however, right?

Alternatively I see this guy:

Also really inexpensive, but gets our 'body' OD up to almost 2" So, what does everyone think?

I'm leaning toward the 3 piece cheap thrust-bearings were the snap-ring is located on the original drawing (basically, at the back of the holder).
 
ErichKeane said:
I found some needle-bearings, how do we feel about using some inexpensive needle bearings
Click to expand...
If I understand the operation of the broach, wobble is going to override the use of circumferential (axial) bearings. The driving unit is rigidly attached to the chuck and the driven unit wobbles in a known pattern to broach the hole. Axial bearing will limit this wobble to the failure of the bearings. Or conversely the driving unit is fixed by the tool post and the driven unit wobbles in the work mounted in the chuck. Or am I missing something?
 
T Bredehoft said:
If I understand the operation of the broach, wobble is going to override the use of circumferential (axial) bearings. The driving unit is rigidly attached to the chuck and the driven unit wobbles in a known pattern to broach the hole. Axial bearing will limit this wobble to the failure of the bearings. Or conversely the driving unit is fixed by the tool post and the driven unit wobbles in the work mounted in the chuck. Or am I missing something?
Click to expand...
The wobble is introduced by the 1 degree angle in the base. The "body" and broach are supposed to remain concentric.
 
It's a stupid simple concept, that AVE video shows just how simple it can be. Don't misunderstand, I want a beautiful, precision tool to hold in my hand (I mean that in a totally straight way) and this is where we have to mince ideas. It would be difficult to screw up, other than poor machining skills, but I'd like to complicate it enough where it has longevity.
 
ErichKeane said:
Great! I'll count you in!

I think we're going to end up doing a decent amount of changes to the design. I think getting us onto an axial and thrust bearing is a good idea. I found some needle-bearings, how do we feel about using some inexpensive needle bearings? Are there any downsides we should be aware of for those?

Next, I like the idea of a 'round flange' instead of the 2 bolt flange on the original design. I suspect that many of us are going to have trouble getting that sort of profiling done accurately enough.

For bearings, does anyone think needle bearings are a bad idea? I found this set (and some others of the same size) that could be pretty cheap: https://www.amazon.com/dp/B082PCTQ2...aWNrUmVkaXJlY3QmZG9Ob3RMb2dDbGljaz10cnVl&th=1

I THINK it means the 'broach holder' would have to be pretty accurately manufactured however, right?

Alternatively I see this guy:

Also really inexpensive, but gets our 'body' OD up to almost 2" So, what does everyone think?

I'm leaning toward the 3 piece cheap thrust-bearings were the snap-ring is located on the original drawing (basically, at the back of the holder).
Click to expand...
I thin that those sets of bearings are turned the wrong way. Don't we need them axial not radial?
 
GunsOfNavarone said:
I thin that those sets of bearings are turned the wrong way. Don't we need them axial not radial?
Click to expand...
I think we need both axial and radial. We could consider going with a tapered roller bearing to get us both (though, only in 1 direction for axially), but I think they are going to be too large.

The idea was to use those bearings up front to control riadial load, then on the 'back' use a thrust bearing [0] between the holder and the body.


[0] Something like these :https://www.amazon.com/ToToT-Bearin...cphy=9032901&hvtargid=pla-1186693713496&psc=1
 
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