# Home Built Rotary Broach



## jumps4 (Aug 22, 2012)

I ran across this site this morning and thought others would be interested. this looks easy to build and the cutters would be affordable to make also. the site is "Mikesworkshop" and has a lot of mods and interesting information. check out his homemade broach and watch the video at the bottom, it seems to work very well.
http://mikesworkshop.weebly.com/rotary-broaching.html
steve


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## 7HC (Aug 22, 2012)

jumps4 said:


> I ran across this site this morning and thought others would be interested. this looks easy to build and the cutters would be affordable to make also. the site is "Mikesworkshop" and has a lot of mods and interesting information. check out his homemade broach and watch the video at the bottom, it seems to work very well.
> http://mikesworkshop.weebly.com/rotary-broaching.html
> steve



Rotary broaches always seem like some kind of machining magic to me!

Good link, I like Mikesworkshop, he's got some good stuff on there.

M


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## PurpLev (Aug 22, 2012)

Thanks for the post , some interesting things there. will have to check it out again later.

am curious about rotary broaching, never heard of it before, and it was interesting to see that it is performed with the lathe running.


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## jumps4 (Aug 22, 2012)

I'v looked at rotary broaches online and the price is wild, this is for the home shop where your not going to be using it to make thousands of holes. it will do square also if you make the cutter. but i'm sure the cutter will take more force for a square hole.
steve


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## PurpLev (Aug 22, 2012)

here's a visual how a square drill works:
[video=youtube;L5AzbDJ7KYI]http://www.youtube.com/watch?v=L5AzbDJ7KYI[/video]


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## 7HC (Aug 22, 2012)

Froneck said:


> Square broach with pilot drill on eBay for $40
> 
> Frank



Got a link?

I found a bunch of hex ones too at the same price, though no pilot drill .  
The rotary 'wobble' holders are in the $300 range, and you can get a kit of assorted hex and square broaches plus the holder for $600.

http://www.ebay.com/sch/i.html?_nkw...odkw=rotary+broach+holder&_osacat=0&_from=R40


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## pjf134 (Aug 22, 2012)

The company in Pittsburgh that makes the rotary broaches for square, hex ect. is called Watts I believe. Prices are high, but they do work. a asia company is now making them and most likely for less money.
Paul


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## Tony Wells (Aug 22, 2012)

I've only used Slater, but they do work. In harder materials, it does take considerable pressure. Seems like too much for a BP type mill, but in the lathe, a tailstock provides enough.


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## jumps4 (Aug 22, 2012)

my point here was if you wanted to try to build your own
like for "hobby machinist" use   lol
steve


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## 7HC (Aug 22, 2012)

jumps4 said:


> my point here was if you wanted to try to build your own
> like for "hobby machinist" use   lol
> steve



Yeah, I get it, but it's always interesting to see the commercially available product and how it's priced.
That only increases the desire to build your own! )

The commercial broach holders allow the bit a certain amount of out of axis movement which I always thought was necessary for the bit to climb around inside the hole.
Unless I'm missing something, Mike's one only allows the bit to rotate and yet it still seems to do the job.
Can someone explain for me?

Thanks,

M


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## jumps4 (Aug 22, 2012)

7hc
right under his drawing he explains about the 1 and 2 degree sides to the holder. he is holding the cutter 1 degree off center when he adjusts the tool holder position. see the angles in the corners.
steve


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## Bill Gruby (Aug 22, 2012)

The 1 degree offset gives you free rotary motion. The bit holder needs room to move.

 "Billy G"


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## jumps4 (Aug 22, 2012)

when i get the time I'm going to try to make one that will fit in my qctp boring bar holder just for fun.
I have some o1 1/2" tool steel for cutters.
steve


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## 7HC (Aug 22, 2012)

I did read the part about angling the sides one and two degrees, but I didn't understand the significance.  

Ok, I re-read it and it's becoming clearer.  
You experienced  guys can visualize what's going on a little better than I can.........but I'll get there in the end!

M


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## jumps4 (Aug 22, 2012)

I'm a complete novic also
I went to cnc because I can draw easier than work the machine  I always end up turning the crank the wrong way or something:whistle:
steve


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## Bill Gruby (Aug 22, 2012)

I don't know anything about this brand but at this point it's going cheap.

http://www.ebay.com/itm/Somma-Tools...075?pt=LH_DefaultDomain_0&hash=item3cc9e064eb

 "Billy G":thinking:


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## 7HC (Aug 23, 2012)

Bill Gruby said:


> I don't know anything about this brand but at this point it's going cheap.
> 
> http://www.ebay.com/itm/Somma-Tools...075?pt=LH_DefaultDomain_0&hash=item3cc9e064eb
> 
> "Billy G":thinking:



At the moment it is, even with the huge markup on shipping.  :huh:

M


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## 7HC (Aug 23, 2012)

I have a broaching question!

For square, hex, oct, star, etc. broaching, you first drill a slightly undersized hole in the workpiece, no problem.

What kind of starting point do you use for a 'D' shaped broach?   

It has to be central in the workpiece, and drilling  a hole will remove material where the flat of the 'D' needs to be.  :thinking:

Thanks,

M


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## Tony Wells (Aug 23, 2012)

I haven't looked, but actually I'd be a little surprised if you could wobble broach a d-hole. Rotary broaches are pretty limited on the amount of material they can remove to bring in the desired profile. A d-hole would have to be drilled just under the flat to centerline dimension, and on most, that would leave quite a bit of material to remove. I have my doubts. I've done and seen a good bit of wobble broaching, and there's a little more to it than meets the eye if you want the tooling to last, and make any time on the parts. Also, the finish of the flats (or whatever shape) isn't all that slick, at least in the materials I've worked with. I've done D-2, 4140/42, 660 Bronze, Aluminum Bronze, and BeCu. It's a slick process, no doubt, but it's hardly prefect.


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## 7HC (Aug 23, 2012)

Tony Wells said:


> I haven't looked, but actually I'd be a little surprised if you could wobble broach a d-hole. Rotary broaches are pretty limited on the amount of material they can remove to bring in the desired profile. A d-hole would have to be drilled just under the flat to centerline dimension, and on most, that would leave quite a bit of material to remove. I have my doubts. I've done and seen a good bit of wobble broaching, and there's a little more to it than meets the eye if you want the tooling to last, and make any time on the parts. Also, the finish of the flats (or whatever shape) isn't all that slick, at least in the materials I've worked with. I've done D-2, 4140/42, 660 Bronze, Aluminum Bronze, and BeCu. It's a slick process, no doubt, but it's hardly prefect.



I don't know if it's a wobble process, but rotary broaches are available for both D and Double D profiles.
I guess it would be used to engage a shaft with a flat, but I was just wondering how it would be started, as a circular starter hole would remove metal that was required for the profile.





Thanks, 

M


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## Tony Wells (Aug 23, 2012)

Oh, it's a wobble process. If you get to make one, or see one on action, you'll see what I mean. I guess they just figure they will be able to move the material. I'd expect it to take much more thrust. I wouldn't want to try it on tough materials. I've tried a simple 3/16" hex in 17-4 H900 and it took a lot of pressure. And the result was blown out burrs on the exit hole and a rough finish through.


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## 7HC (Aug 23, 2012)

Bill Gruby said:


> I don't know anything about this brand but at this point it's going cheap.
> 
> http://www.ebay.com/itm/Somma-Tools...075?pt=LH_DefaultDomain_0&hash=item3cc9e064eb
> 
> "Billy G":thinking:



I rather think you've started a bidding war!   :lmao:



M


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## jumps4 (Aug 23, 2012)

in the pic of the ebay item you can see the tool holder is off center this is not set to one side but at a different angle from the spindle axis by about 1 degree
steve


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## 7HC (Aug 24, 2012)

jumps4 said:


> in the pic of the ebay item you can see the tool holder is off center this is not set to one side but at a different angle from the spindle axis by about 1 degree
> steve



That must have been one special used broach holder, it just sold for $400 inc shipping; which is interesting because you can buy a brand new one (different make) of the same size for $325 inc shipping! :thinking:

http://www.ebay.com/itm/NEW-Basic-R...=261084964075&ps=63&clkid=1555671043669867512


M


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## Hawkeye (Aug 24, 2012)

If you're looking for something more for the hobby machinist, take a look at LMS. They have wobble broaches in the $35 range, with MT2 holder for $80 and R8 holder for $100 (shown in the catalog only).

You could make a holder based on what we've learned on this thread and buy the cutters as needed.

http://littlemachineshop.com/products/product_search.php?critFast=rotary+broach&B1=Product+Search

Actually, you might have to make your own holder. They don't seem to list them on their site. From what I've seen, most wobble broaches have a 1/2" shank, but the LMS ones appear to be more like 1/4". The largest they carry is 3/8", in hex and square.


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## jumps4 (Aug 24, 2012)

nice piece of info thanks mike
thats in the range of my budget if my home built efforts dont work out
steve


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