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Fasttrack
12-18-2008, 03:45 PM
The other thread got me thinking... has anyone tried to make their own rotary broach tool holder? I saw Frank Ford's website where he makes his own 3/8" hexagonal rotary broach, but I was wondering if anyone made the actual tool holder.

Seems like it's fairly simple in principle but might be difficult to build one that stands up to the pressures involved. I reckon the big sticking point would be getting a good (i.e. expensive) bearing. No $5 chineese bearing... :) That and the taper if you weren't familiar with cutting tapers.

I've got plenty of projects on my plate, but I was sort of thinking about drawing up some plans in my new Autodesk Inventor 2009 and putting them in a folder for later...

<edit> oops - that should read "making a rotary broach" ... me speek good anglish ;)

jacampb2
12-18-2008, 04:11 PM
I had the same thoughts after seeing the other thread. It looks like an interesting process. I would not want to spend the $1k plus on a head though. From what I gather via google, the head holds the tool at a 1 angle, and is free to rotate w/ the work causing a sort of wobbling action. Seeing how it works, and understanding how to make it are two different things though :D

Hopefully one of our genius types will chime in.

Later,
Jason

jim_geib
12-18-2008, 04:55 PM
I think ther was a write-up in one of the two mags about it. I will look tonight and see if I can find it.




Jim Geib

hornluv
12-18-2008, 04:55 PM
They had an article in the Sept./Oct. 2002 issue of HSM on doing just that. The article was a little light on the construction details, but I think it would give you a good starting point.

Edit: I added the year to the issue. That would have helped initially.

Fasttrack
12-18-2008, 05:09 PM
Dang - I get Machinist Workshop, not HSM... Thanks for the encouragment though! At least it doesn't sound too ridiculous to build.

Teenage_Machinist
12-18-2008, 05:10 PM
What exactly is rotary broaching anyway? Will it let me make hex blind holes?

I frankly find it a bit inexplicable that the tools are so insanely expensive. I do not know of any other sort of tooling that is that size and precison and yet costs so much.
Edit: wait which issue? I do not remember ANYthing on rotobroaching this year.

FatWheels
12-18-2008, 05:38 PM
My suspicion is that were I to set out to build a rotary broach, I might be better off trying to NOT build a rotary broach and using cheap bearings to boot. I'd have that 1 degree wobble for sure:D :D I wonder if that's how the inventor stumbled onto the design in the first place. The cutting action of a rotary broach seems not all that intuitive in the first place.

cheers,

Jim

jacampb2
12-18-2008, 05:47 PM
Here is an interesting article on the math behind the early precursor to what is being done now. It appears, according to this article, that one of the early inventors was Harry Watts, who deigned bits to drill square, hex and octagonal holes all the way back in 1914. The method is different, as seen in the article, but a neat read, none the less.

Doh! Edit for link: Clicky (http://upper.us.edu/faculty/smith/reuleaux.htm)

Later,
Jason

hornluv
12-18-2008, 05:49 PM
Sorry, it was the Sept/Oct 2002 issue of HSM. I got distracted and forgot to put the year down. It's a blue cover with the lead article "Gear Repair by Bronze Surfacing".

millhand
12-18-2008, 05:56 PM
I built an ORB tool using two 7R-10 bearings (5/8" bore) that were sitting around waiting to be used. The spindle was 0.625" through the bearings and extended 1/2" beyond the bearings at 3/4" diameter to accommodate a set screw to retain the cutting tool which has a 0.250" diameter. The hole for the tool is drilled and reamed into the spindle at a 1 deg angle. This differs from the commercial units: Slater and Somma build the 1 deg angle into the mounting plate which also has adjustment screws to center the tip of the cutter. This detail is important: the tip of the cutter is centered with a dial indicator so that it aligns with the hole in the workpiece. My simpler unit did not incorporate this: I centered the cutter by putting a spacer behind it. There is a lot of thrust while cutting and the set screw will not retain the tool axially.

The hex sides of the tool were ground at 3 deg clearance. The cutting face of the tool was ground with some "back rake" with a ball burr in a die grinder mounted to the tool and cutter grinder wheelhead.

This tool made 3 special socket head cap screws in brass at .220" across the flats to fit a 7/32" Allen wrench. A later attempt to make a 9/64" hex in O2 tool steel failed: not enough thrust to make the cut. I do not know if making the tool with the Slater/Somma type of offset mounting would have been successful. Someday when I run out of other projects I might make that version.

Carl

Fasttrack
12-19-2008, 12:33 AM
Sorry, it was the Sept/Oct 2002 issue of HSM. I got distracted and forgot to put the year down. It's a blue cover with the lead article "Gear Repair by Bronze Surfacing".


Ahhh - I believe I actually have that issue due to the generosity of one of our board members! I'll check it out when I get home. Thanks!

Jason - That is actually how I was first introduced to "rotary broaching". I got into blacksmithing when I was younger and bought up all kinds of books on the subject. One has a very interesting chapter specifically on the "Watt's Drill Bit" for cutting square holes. Very cool stuff.

Carl - Cool! At least I know it can be done and I know what to look out for!

Ken_Shea
12-19-2008, 01:07 AM
This would be a very interesting and popular project.

They incorporate thrust bearings as well as radial bearings.

jacampb2
12-19-2008, 10:01 AM
Anyone have some good close pictures of a production head? It may help determine design. It seems most suppliers don't show much in the way of pictures...

Teenage_Machinist
12-19-2008, 10:58 PM
I find the commercial ones inexplicably expensive. The things cost like facemills. Big facemills.

Somebody get a toolmaker's universal vise and make one, should be doable. I may try it. The bearings would need to be good but not like grinder bearings. Timken type might be good.

HSS
12-22-2008, 11:17 PM
How bout a good close picture like this?http://i267.photobucket.com/albums/ii285/goochiepepper/DSC00213.jpg
http://i267.photobucket.com/albums/ii285/goochiepepper/DSC00215.jpg
http://i267.photobucket.com/albums/ii285/goochiepepper/DSC00216.jpg
http://i267.photobucket.com/albums/ii285/goochiepepper/DSC00214.jpg

jacampb2
12-23-2008, 12:58 AM
What exactly are we looking at here? Those don't look like the rotary broach heads that I have seen on line? Can you explain?

Thanks,
Jason

sconisbee
12-23-2008, 02:53 AM
See here for an older discussion on it and a holder design, havent got much time now will try to check back later, will email plans if anyone is interested.

http://bbs.homeshopmachinist.net/showthread.php?t=27232

jacampb2
12-23-2008, 03:42 AM
See here for an older discussion on it and a holder design, havent got much time now will try to check back later, will email plans if anyone is interested.

http://bbs.homeshopmachinist.net/showthread.php?t=27232


Awesome! It seems we are trying to reinvent the wheel with this thread, you already went through it once. I don't know how I missed it the first time around...

Did you ever get your head finished? As for making the broaches, how critical is the relief angle? I realize it has to be enough to clear the bore while running in at an angle, but is this a job you can do by hand, or does it have to be done on a grinder? The recent post about making the broaches themselves, showed the hex tool being made on a grinder. I have access to nothing but my mills (which I could conceivably make a arbor and install a grinding wheel for this simple project) or a standard bench grinder. Is that outside of the realm of possibility?

Thanks for taking the time to point us in the right direction.

Thanks,
Jason

JCHannum
12-23-2008, 08:25 AM
What exactly are we looking at here? Those don't look like the rotary broach heads that I have seen on line? Can you explain?

Thanks,
Jason
The photos in HSS's thread are mechanical keyway cutters. I forget the manufacturer, but the spindle drives a small cutter at the bottom end to cut the keyway in the bore.

vinito
12-23-2008, 12:57 PM
.......... ..
Sorry, not worth posting in retrospect...

lane
12-23-2008, 08:21 PM
I took some apart at work and have been making up a set of drawings to build them . They are not that fancy in side . But use a large needle bearing about an inch in diameter and a thrust bearing. If I can get around to finishing the drawings I will post them. Ther will take a 1/2 inch dia broach which can be made from a 1/2 dia broke end mill shank. I make them all the time at work. All you need is a spin fixture on a surface grinder with a sine plate.

Fasttrack
12-23-2008, 08:53 PM
All you need is a spin fixture on a surface grinder with a sine plate.


:D

Looks like I need to buy a surface grinder :) The drawings would be awsome! I'll get around to drawing some up at some point in time, otherwise. I wonder if a tapered or angular contact bearing could take the place of the thrus and needle bearing. I guess it would add some bulk to the head.

Teenage_Machinist
12-23-2008, 10:50 PM
Or you could use carbon steel, mill the angles pre-hardening.

I think the most useful size would use 3/8 or 1/2 shank, timken bearing if it can be had that small. Or a 2mt shank woudl be a useful size, if you can design one for mini-machines.

Mcgyver
12-23-2008, 11:24 PM
:D

I wonder if a tapered or angular contact bearing could take the place of the thrus and needle bearing. I guess it would add some bulk to the head.

without cylindrical grinding apparatus, I wouldn't go with needle bearings. Needle bearings need hardened shafts. there's lots of ways to handle thrust/radial loads as you point out...basically you're constructing a spindle but it doesn't need super accuracy and the thrust is one direction only....what about two deep grooves, one at each end, and a thrust bearing? agreed it'll add bulk though

My perception is that there's a lot of thrust - is that correct? heavy duty thrust bearings required? maybe cylindrical? just guessing, never used one or have one apart

Fasttrack
12-24-2008, 12:30 AM
My perception is that there's a lot of thrust - is that correct? heavy duty thrust bearings required? maybe cylindrical? just guessing, never used one or have one apart


Same here - I was contemplating the smaller tapered roller bearings from an old rear end. I was imagining this for my Pacemaker, so it'd have a 4 MT mount and I don't think the size of the bearing would be too ridiculous.

Good thing about HSS for the broaches is that there is an almost endless supply of dull 1/2" endmills that aren't worth re-sharpening (at least as an endmill) ;)

Teenage_Machinist
12-24-2008, 02:08 PM
McMaster Carr: 1 inch ID, about 2 inch OD Tapered Rollar Bearing has 1570 radial and about a thousand thrust Dynamic Load Cap, Needle Thrust Bearings 1 inch ID cost much less, are in washer form, and have a limit of 3000 about pounds, Ball Thrust Bearings are quite thick and have a cap of 5000 pounds. One way would be to use the taper bearing and then have an auxilliary thrust bearing, but that would be unpreloadable,.

lane
12-24-2008, 06:52 PM
Just use a small wheel bearing off a boat trailer . even Wal -Mart has them. You fellows get carried away about bearings . They are not that special. any will do.

peter08
12-26-2008, 04:21 PM
Here's some great pictures of rotary broaching tools:
http://www.rotarybroaching.com

DR
12-26-2008, 05:08 PM
.....................................

My perception is that there's a lot of thrust - is that correct? heavy duty thrust bearings required? maybe cylindrical? just guessing, never used one or have one apart

Maybe not as much thrust as you might think.

This is a guess from my experience rotary broaching 5/32 hexes in 12L14 with Slater heads. About 500 pounds force needed.

My guess is based on using the heads in three different machines, one being hydraulic with a method of varying turret force.