Poor mans slotting head

[timo_gross]

Blind hole keyways are usually terminated with a hole slightly over the key size. This maintains the structural integrity of the unit being keyed. Undercutting can lead to failure at the undercut.

Did not get it at first. Drill the hole 90° to slotting direction and all of a sudden it makes sense.

 

[76dave]

For a blind hole, have you considered using a rotary wobble broach. A simple design for one is shown at "mikesworkshop.weebly.com"

 

[dazz]

Hi
It is easier/faster for me to make a tool for my slotter than than a wobble broach. In addition, a slotting tool is far more versatile.
For a blind hole a wobble broach would still need clearance at the base of the hole.

 

[timo_gross]

For a blind hole, have you considered using a rotary wobble broach. A simple design for one is shown at "mikesworkshop.weebly.com"

Hello,
yes and no. Yes I had a look into rotary broaching. No I did not even try a key way in blind holes or rotary broaching a keyway.
Before I continued working on the slotting head, I found this link:

https://www.polygonsolutions.com/ro...-rotary-broaches/double-keyway-rotary-broach/
It gives some background information on the rotary broaching. I abandoned the idea of using a rotary broach (for that particular task). For some smaller squares or hex a rotary broach is nice to have.
Rotary broaches are limited in depth, as far as I know.

Greetings Timo

(p.s. I am not sponsored or related to this company, just found their explanation to be useful)

 

[Alec Ryals]

use the mill guill by hand

 

[timo_gross]

use the mill guill by hand

Yes, sometimes an option. But ... the mill in question does not even have a quill . It looked like this at some point.

Running the stepper motor driven head up and down is very slow, it would take forever. (do not ask why I know this )

 

[Ozwes007]

Rotary broaching is a nice technic. Made one to put a dodecahedron hole through some gears for a gearbox I made years ago. Tooling can be costly to make though, depends on what you are cutting.

 

[william_b_noble]

you may find this useful: How Rotary Broaching Works by Polygon Solutions
commercial rotary broaches aren't terribly cheap when new but they will make your square/hex/splined hole really efficiently

 

[wazrus]

Keyway broaching usually implies a nice, expensive - and easily broken - 'push' broach. Industrial convention is that broaches should be 'pulled' and that's OK if you have the wherewithal/space etc. My broaching is 'pushed' and the broaches I make myself. Push broaching is sort of asking for broken broaches, so it's a matter of support for the broach, more than anything else. My shop made broaches are simply bits of rectangular HSS - readily available - with teeth cut using a cutting disc in an angle grinder rigidly mounted and the work (the broach blank) is reciprocated underneath. Of course, the blank is packed or the grinder is lowered to have the tooth depth where you want it. The cutoff disc will do quite a good job and do it quite quickly. Once the teeth are cut. it's a fairly simple matter to 'angle' the disc to grind a little relief on the crown of each tooth. The teeth are not unlike those on a circular saw, but without the 'set'. Chip clearance isn't quite the same issue it is with a circular saw, so 'set' isn't necessary, nor is side rake. The 'support' comes from a broach 'body' of round MS, with a groove to suit the HSS broach blank milled along it. It will probably be a very deep groove, so it takes a,little more time to have it deep enough for the HSS blank to pretty much disappear. I found the easiest way to 'set' the depth of cut was to angle the groove bottom, so the broach will cut about .015" at each pass. A few .015" metal packing strips underneath the broach body, in the groove, will have pretty reasonable keyways. My 'broaches' are only about 6" long, so the depth of cut is a bit limited. I have broaches for 1/8", 3/16" and 1/4" and 3,4. 5 and 6mm and bodies of 12, 13, 14, 15, 16, 18, 19 and 20mm. The body 'fir' doesn't have to precisely suit the hole, so, for instance, 19mm is quite OK for 3/4"

 

[deverett]

Keyway broaching usually implies a nice, expensive - and easily broken - 'push' broach. Industrial convention is that broaches should be 'pulled' and that's OK if you have the wherewithal/space etc. My broaching is 'pushed' and the broaches I make myself. Push broaching is sort of asking for broken broaches, so it's a matter of support for the broach, more than anything else. My shop made broaches are simply bits of rectangular HSS - readily available - with teeth cut using a cutting disc in an angle grinder rigidly mounted and the work (the broach blank) is reciprocated underneath. Of course, the blank is packed or the grinder is lowered to have the tooth depth where you want it. The cutoff disc will do quite a good job and do it quite quickly. Once the teeth are cut. it's a fairly simple matter to 'angle' the disc to grind a little relief on the crown of each tooth. The teeth are not unlike those on a circular saw, but without the 'set'. Chip clearance isn't quite the same issue it is with a circular saw, so 'set' isn't necessary, nor is side rake. The 'support' comes from a broach 'body' of round MS, with a groove to suit the HSS broach blank milled along it. It will probably be a very deep groove, so it takes a,little more time to have it deep enough for the HSS blank to pretty much disappear. I found the easiest way to 'set' the depth of cut was to angle the groove bottom, so the broach will cut about .015" at each pass. A few .015" metal packing strips underneath the broach body, in the groove, will have pretty reasonable keyways. My 'broaches' are only about 6" long, so the depth of cut is a bit limited. I have broaches for 1/8", 3/16" and 1/4" and 3,4. 5 and 6mm and bodies of 12, 13, 14, 15, 16, 18, 19 and 20mm. The body 'fir' doesn't have to precisely suit the hole, so, for instance, 19mm is quite OK for 3/4"

Any chance of showing us a few pics of your home made broaches, please?

Dave
The Emerald Isle

 

[William May]

Keyway broaching usually implies a nice, expensive - and easily broken - 'push' broach. Industrial convention is that broaches should be 'pulled' and that's OK if you have the wherewithal/space etc. My broaching is 'pushed' and the broaches I make myself. Push broaching is sort of asking for broken broaches, so it's a matter of support for the broach, more than anything else. My shop made broaches are simply bits of rectangular HSS - readily available - with teeth cut using a cutting disc in an angle grinder rigidly mounted and the work (the broach blank) is reciprocated underneath. Of course, the blank is packed or the grinder is lowered to have the tooth depth where you want it. The cutoff disc will do quite a good job and do it quite quickly. Once the teeth are cut. it's a fairly simple matter to 'angle' the disc to grind a little relief on the crown of each tooth. The teeth are not unlike those on a circular saw, but without the 'set'. Chip clearance isn't quite the same issue it is with a circular saw, so 'set' isn't necessary, nor is side rake. The 'support' comes from a broach 'body' of round MS, with a groove to suit the HSS broach blank milled along it. It will probably be a very deep groove, so it takes a,little more time to have it deep enough for the HSS blank to pretty much disappear. I found the easiest way to 'set' the depth of cut was to angle the groove bottom, so the broach will cut about .015" at each pass. A few .015" metal packing strips underneath the broach body, in the groove, will have pretty reasonable keyways. My 'broaches' are only about 6" long, so the depth of cut is a bit limited. I have broaches for 1/8", 3/16" and 1/4" and 3,4. 5 and 6mm and bodies of 12, 13, 14, 15, 16, 18, 19 and 20mm. The body 'fir' doesn't have to precisely suit the hole, so, for instance, 19mm is quite OK for 3/4"

All my broaches are push broaches, that is all I have ever used. I have guides and shims in sets for them all and have never had one break. Are you push broaching with no guide and no shims? I have from 1/16" up to 1" in slotting, hexes, and squares, and have never had a problem. Are you using some lubricant? Bill

 

[timo_gross]

All my broaches are push broaches, that is all I have ever used. I have guides and shims in sets for them all and have never had one break. Are you push broaching with no guide and no shims? I have from 1/16" up to 1" in slotting, hexes, and squares, and have never had a problem. Are you using some lubricant? Bill

How do you push the broach? I am asking, because I made a diy broach and then came to the conclusion that it would require some sort of proper press to use it. Doing it with the drill press worked barely and it did not "feel right".
I do not have any press in the workshop.

I rotated a workpiece a little bit at a time, then made a tiny slot at a time . Not a single keyway just tiny slots.


Of course one slot ended up too big.

But it was a proof of concept and it works.

Greetings Timo

 

[wazrus]

Attache are pikkies of the homemade broaches. I do not have many 'bought' broaches, as they are so expensive, at least in Australia - where everything is expensive. I have one short commercial broach: any takers? And I do have all the gear for the commercial broaches and I do 'push' them in use. However, 'my' broaches have stood all the rigours of use in all sorts of material. The pix show some flame-cut, from 3/4"x6" mild steel wheels. The broach drive is from a 3T mandrel press and while this may sound a little underwhelming, it's simply a matter using thinner shims, if the going is a bit tough. For final sizing, I have a collection of thicker shims and when I'm near the depth required, I swap to the thicker bit and then finish off the lot with that shim. The broaches are quite simply sharpened in the same setup I used to cut the teeth. By the way, 'quarter' my loco drivers using the keyways: once cut, it's all 'automatic'!

 

[SmithDoor]

Attache are pikkies of the homemade broaches. I do not have many 'bought' broaches, as they are so expensive, at least in Australia - where everything is expensive. I have one short commercial broach: any takers? And I do have all the gear for the commercial broaches and I do 'push' them in use. However, 'my' broaches have stood all the rigours of use in all sorts of material. The pix show some flame-cut, from 3/4"x6" mild steel wheels. The broach drive is from a 3T mandrel press and while this may sound a little underwhelming, it's simply a matter using thinner shims, if the going is a bit tough. For final sizing, I have a collection of thicker shims and when I'm near the depth required, I swap to the thicker bit and then finish off the lot with that shim. The broaches are quite simply sharpened in the same setup I used to cut the teeth. By the way, 'quarter' my loco drivers using the keyways: once cut, it's all 'automatic'!

I was lucky at time had the money and have 2 sets. I also have arbor press for the broach and press bearing in.

Even going to auctions they are costly.

The other way is use a end mill and mill a slote in bore and use a round key.

Most do not know if read some old books a complete machine shop can make gear key to shaft. So you a lathe , mill with dividing head and a broach or shaper. Did you most machine shops today can do that today. They send out for at less the broaching or cutting the gear.

Getting back how this a hobby shop setting.
The best I came up with is use a gear motor and crank to quill of a mill maybe at most a 1" [25mm] stork.
A short stoke needs less power.

Dave

 

[Vietti]

Perhaps I missed it, but I find broaching much easier if I drill a hole where the key way will be, use a sacrificial bushing to keep things straight.

 

[wazrus]

I have to confess an omission, in that I had written about 'my' broaches in 2013! Nothing else has changed, though. i simply didn't look to page 1 of these posts.

 

[mcostello]

Rotary broaches do not need clearance at the bottom of the hole. Was in a shop that rotary broached 1/2" holes about 1/2 " deep in 17-4 SS, no clearance hole allowed . Chips were a pain to break off.

 

[William May]

How do you push the broach? I am asking, because I made a diy broach and then came to the conclusion that it would require some sort of proper press to use it. Doing it with the drill press worked barely and it did not "feel right".
I do not have any press in the workshop.

I rotated a workpiece a little bit at a time, then made a tiny slot at a time . Not a single keyway just tiny slots.
View attachment 139791

Of course one slot ended up too big.
View attachment 139793
But it was a proof of concept and it works.

Greetings Timo

I have a small Dake press that I use for my small broaches. It has a hand lever to operate it. have a larger one for bigger broaches, and then a hydraulic press for the really large ones. Once your broach and workpiece are set up, the forces really should not be that great. A broach typically takes off perhaps .005 (or less) with each tooth. So a lubricant, and gentle pressure and things go very sweetly. Just make sure to use a guide, even if you have to machine one special to the job. This is not normally necessary, as broach kits usually have the guides included with them. Just make sure you use lubricant, make sure the broach is square and plumb to the hole, and go gently. Your broach will soon plop gently onto the rags placed under the dake press, and you will have another fine hole.

 

[wazrus]

I usually use a 3 ton mandrel press, which uses a simple, (about 1-1/2" square rack, and its mating gear is on the handle shaft. i have another 1 tonner for smaller stuff. I often use a piece of pipe over the handle bar to increase leverage if needed. I've not counted, but i think my 'home' broaches have about 20 teeth, which are 'set' to cut .015" at a pass. i clear chips, which curl into the tooth gullets, with the MK1 human fingernail. Hard on the manicure, though. As Wlliam said, the broach drops through underneath for you to catch..