Rotary Broach Plans?

Hello all,

I was wondering if anyone had plans to make a rotary broach system? I don't really have a need for one at the moment, but it sure seems like they could be very handy to have! I'm guessing they are pretty simple, but I have never seen one taken apart.

Thanks in advance!

Tyler

Slater makes one for screw machines and there is one for mills, but I do not recall the makers name ansd I should as I have a few of them.

Frank Ford is a member here and has a nice little article (link) on his website about making a rotary broach.

rotory broach

use the search app .there has been so detailed threads on the subject

Rotary Broach plan for cutting square holes

attached zip file has Adobe Acrobat reader pdf of plan for a plain bearing rotary broach.

they cut by shank end wobbling as tip of broach does not rotate (when used on a mill.)..... basically like drilling a square hole ( you do need a pilot hole)
also chips get pushed forward. Broach uses 6 each setscrews to adjust on a vee block so tip does not wobble.

professional rotary broach is around $1500 and broach bit around $150.

i made 0.380 square broach out of drill rod on a milling machine with a 5C collet indexer and hardened with a torch and tempered with a toaster oven.

i would not use a plain bearing one for 24/7 constant professional use but if you only want to make maybe 1 square hole a week i am guessing it will last for awhile.

TomB,
Thanks for the detailed drawing! I've seen rotary broaches in operation, but I never had the chance to take one apart and measure the offsets and declinations and I don't have the time to experiment with trying various combinations.
Your drawing looks like it provides a great starting point. I think I'll try building it and add case hardening to the wear surfaces.

One thing to keep in mind is that the rotary broaches take a lot of axial thrust to work, so on smaller lathes you'll be restricted to pretty small holes.

The Slater site has a table that shows the thrust required for typical holes in a range of materials, be seated when you look at it, and if you have a weak heart, don't look at it at all.

Paul T.

georgeL said:

TomB,
Thanks for the detailed drawing! I've seen rotary broaches in operation, but I never had the chance to take one apart and measure the offsets and declinations and I don't have the time to experiment with trying various combinations.
Your drawing looks like it provides a great starting point. I think I'll try building it and add case hardening to the wear surfaces.

Click to expand...

I was looking at this and considering the thrust forces I was wondering if this design doesn't have high friction? Couldn't a tapered roller bearing be worked into the design somehow?

Rotary Broach Plan update and info

updated rotary broach plan with more dimensions

thrust on Bridgeport mill creating 3/8" sq in Alum (13/32 pilot hole) was fairly high at 50 rpm but at 200 rpm it was moderate, about like drilling a 5/16" hole with no pilot. Moderately easy. I looked up recommended speeds and it is 2000 rpm which I would think the force required would be less and broach time faster.

Since the broach I made was from o-1 drill rod (not HSS) I would go less than half the recommended speed so broach bit does not get as hot and broach bearing does not get as hot.

Grease probably should be one with moly in it or rated for extreme pressure. My opinion is it is not much different that a lathe dead center rubbing on center hole work piece. With plain bearing broach may only last 100 - 1000 broachings. While not good enough for 24/7 production this would be good enough for occasional use. Probably I would use it mostly for creating a square hole for a socket wrench which I only rarely ever need to do. So spending $1650 is a bit much for a occasional square hole. Yes the design could use a thrust bearing or angular contact bearing but I do not see spending an extra $20 - $200 for bearings for limited use.

In my opinion this would be a good apprentice machinist shop project. I am currently making a plain bearing design broach and I can see it is moderately challenging shop project. I plan on making a bigger rotary broach for 1/2" square holes. It is possible for plain bearing to be a steep taper that would not lock together like a morse taper but steep like a lathe tailstock dead center. I plan on testing a few different designs.

I'm surprised some company hasn't introduced a lower cost rotary broach for occasional non-production use, I'd pop for one for prototyping usage if it was in the $250. to $300. range, which I think is a doable price for a non-production type unit, probably similar to the design posted in this thread.

I tried to talk Slater into considering that but they didn't see enough market for it. I think eventually a cheap chinese one is going to appear and I think Slater would be smart to get a low cost one out first before that happens. But what do I know, I'm still driving around in a '91 Caprice wagon.

Paul T.

Low Cost Rotary Broach Tool Holder

PaulT said:

I'm surprised some company hasn't introduced a lower cost rotary broach for occasional non-production use, I'd pop for one for prototyping usage if it was in the $250. to $300. range, which I think is a doable price for a non-production type unit, probably similar to the design posted in this thread.

I tried to talk Slater into considering that but they didn't see enough market for it. I think eventually a cheap chinese one is going to appear and I think Slater would be smart to get a low cost one out first before that happens. But what do I know, I'm still driving around in a '91 Caprice wagon.

Paul T.

Click to expand...

At Polygon Solutions we offer a rental program on our rotary broach tool holders. For $100 you can rent one of our rotary broach tool holder for 30 days. This is a great option for small jobs or just to try it out. If you want to keep it we just take the $100 rental fee off the original price of $699.

Here is the link if anyone wants more details: Rotary Broach Tool Holder

Cost of Rotary Broach

in my opinion the cost of most Rotary Broaches is too high
.
LittleMachineShop.com - Rotary Broach Tool Holder 2MT
a link to one sold for <$80 and it is usually sold out as they probably are selling 10-100 times more than the higher priced ones. i would imagine they make far more money selling the Broach bits than the Rotary Broach
.
HF in particular sells cheap tools but the consumables that are for the tools are much closer to average price and where they probably get most of their profits from.
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i believe it was Gillete razor company that sold razors cheap as they made their profits from the razor blades.

If this a dumb question please excuse me, but if you want the broached hole oriented in some way, can you rough mill it first, then use the rotary broach to just clean out the corners nice and sharp ?


Bill

hard guide bushing

as an apprentice i learned if you wanted to cut / slot a hole in the field with a hole saw you had to

1) remove hole saw pilot drill
2) clamp on a plate with a hole already in it to guide the hole saw where you want the new hole to be. so cutting 1/2 a hole is easy.
.
with a rotary broach you could clamp on (or use screws) a guide bushing orientated in the desired direction so a square hole would line up. for occasional use the "guide bushing" may not have to be hardened and can be regular steel.
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with a hardened plate with holes in it and clamped on it is possible to drill 1/2 a hole (slot a hole) with a twist drill using a portable drill.
.
an old "field machinist" trick of the trade

To have a rotary broach be 'timed', you use a lathe dog on the broach and something clamped to the work to drive it. That can be as simple as a jaw of the chuck if the stick out is short. I think its Slaters website spells that out in their examples.

rotary broach alignment

Alignment fixture sketch from blog post:

The littlemachineshop link shows it discontinued. Anyone know why?

Thanks,

Clutch

I just emailed LMS about this since they still show a full compliment of square and hex broaches. I'll report back what they have to say.
I've been looking at the Schlitter 5000 swiss machine rotary broach holder which is 5/8" shank and 8mm insert size but I don't dare ask what it costs.

After looking at the posted plans I think I might sacrifice an old live center and the shank and backplate from an adjustable turret tool holder. Milling the required 1.5º angle on the back plate should be easy and pulling the point out of the live center and drilling it out shouldn't be too difficult, meanwhile melding the bearing cup to a front plate also seems quite straightforward.

is that broach tool holder only for lathes or can it be used on mills as well?

They can be used on milling machines also.