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Broach Bushings?

Don’t let these guys scare you. If you have ever hand tapped a hole and know the feeling of it is straight or it is NOT. If not stop correct, once that cutter commits to the metel it’s too late. Be patient and start it right.

Sorry chief. Not trying to scare anyone.

Apples to oranges with the tap analogy. You can start a push broach absolutley square or even the tilted the other way and sometimes it will dig in. Sometimes it will really dig in. If you have a high limit dimension it's not uncommon to be good on the top and over on the bottom.

I've push broached too many holes to recall. Not talking about repair work, but production. Couldn't use one pass production keyway broaches because of odd bore sizes, or stock allowance in bores. When you've got a production lot to broach, using alignment tools, all proper methods, and the broach still sucks, stone a small land and you'll breeze through the rest of those parts.

It's not even scary.
 
I'm adapting two hubs to the 1" diameter rear axle on my daughter's go-kart. This requires me to broach 1/4" keyways in the new hubs. They appear to be cast iron, (or steel).

I have the use of a lathe, a mill, and a press. I've never broached a keyway before, though I understand the process. I have ordered up a broach.

Two questions. One, would the broaching be possible on my one ton arbor press, or will I need to use my hydraulic press?

Secondly, can I get away with making the broach bushing out of aluminum, or does it absolutely have to be steel?? Or would aluminum only work if I made the slot deep enough to require a "bearing shim" on the first pass?

Thanks in advance!!
Vettepilot
 
A 1/4" broach will come with a shim in the package because you would need two passes with the broach. Factory bushings have the slot milled to exactly the correct depth to do the first pass with no shim and the second pass with the factory shim and achieve the correct depth of keyway in your hub. If you make your own bushing, the main trick is to get the depth right. I use a 2 ton arbor press for most of my (small) keyway broaching. The force you need depends on the hub material and the number of passes you take.

I just looked it up and 1/8" to 1/4" broaches come with one shim. You get two shims with 5/16" to 3/8". The idea is to keep the tonnage within the range of a certain size press. Lots of help in this catalog:

Larry
 
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An aluminum broach bushing would be fine, but WHY invent the wheel when you can buy one ready made cheaper than you can machine one for. Broaching DOES have some pitfalls. I've broached thousands of parts at this point, and now try to do everything with production broaches. BUT when broaching with the shorter, cheaper broaches, using the shims is just how it's done. Be sure to watch your broach to make sure it's staying vertical. For some reason they like to cock, which makes it cut deeper and much harder. If it's getting hard to push, pull the part out and look at the bottom and make sure the shoulder of the broach is right up to the front of your keyway- no gaps. If it's going crooked, just tap it back in to straighten it out.

If your hubs are cast iron, it tends to cut easier than steel. Lube the back of your broach so it slides easily past the shim, instead of gripping it, and pushing it with it through your keyway. That ninety degree bend doesn't resist pressure from your arbor press.
 
You already got quite a pile of answers in the other thread... I'll see about getting those answers moved to this one. I see there is also a duplicate new thread... 🤨
 
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Like pecking with a drill bit, push a bit then back off for a second to allow the broach to take a new, straighter position on the ram. Repeat. Lubricate with oil instead of a cutting fluid.

May take a bit longer, but faster than reversing the part or making a new one after waiting for the new broach to be delivered.



Broaching internal keyways is s PITA. I have trouble with the broach cocking in the bushing then the teeth take a hog cut and the KW gets a taper in it. I need to come up with a plan to hold the top of the broach firmly parallel to the bore.
 
Dave, Thanks for the encouragement, but this thread is 14 years old. The keyways I was cutting were cut that long ago and the parts were sold long ago as well.

And the comments don't bother, scare, or even slow me down very much. But I do/did appreciate their answers.

I hope the discussion does help others today. I added a bit from my limited experience above.



Don’t let these guys scare you. If you have ever hand tapped a hole and know the feeling of it is straight or it is NOT. If not stop correct, once that cutter commits to the metel it’s too late. Be patient and start it right.
 
You said, "... stone a small land ...". Do you mean on the top end of the broach?

And what about the bottom surface of the press's ram? Shouldn't that be checked for flatness and perpendicularity to the vertical axis of the press?



Sorry chief. Not trying to scare anyone.

Apples to oranges with the tap analogy. You can start a push broach absolutley square or even the tilted the other way and sometimes it will dig in. Sometimes it will really dig in. If you have a high limit dimension it's not uncommon to be good on the top and over on the bottom.

I've push broached too many holes to recall. Not talking about repair work, but production. Couldn't use one pass production keyway broaches because of odd bore sizes, or stock allowance in bores. When you've got a production lot to broach, using alignment tools, all proper methods, and the broach still sucks, stone a small land and you'll breeze through the rest of those parts.

It's not even scary.
 
. . .You get two shims with 5/16" to 3/8". The idea is to keep the tonnage within the range of a certain size press. . .
I believe the main reason regarding tonnage is not the press since they vary greatly, but to prevent breaking the broach itself. It is also to keep chip volume below gullet volume. That is also why each broach has a max length of cut specified.
 
Very limited experience here, but a 1/4" broach in a cast iron John Deere mower pulley was easy with a 3 ton jet arbor press. It was easier than a 1/8 broach in a steel gear. It was less nerve wracking since the 1/4 broach was more robust. I think you will have clearance problems with a 1 ton press. My 1/4 broach is 12" long.
 
I've done this in my arbor press, it's fast, but I've found for one or two it's easier to just grind a tool and peck away on the Bridgeport. Hold the tool in a collet, and just stroke the quill by hand, shaving off a few thou by advancing the table til you're done. No $ cost or waiting for tools to arrive.
 
You said, "... stone a small land ...". Do you mean on the top end of the broach?

And what about the bottom surface of the press's ram? Shouldn't that be checked for flatness and perpendicularity to the vertical axis of the press?
First let me say I understand the need for proper alignment, a tight press ram that won't tilt, all that stuff. But I also understand sometimes no matter how much care is taken with alignment and procedure, a push broach will hog in at the bottom of the cut. If you've broached very many parts you've seen this happen. Sometimes you can't get the broach to dig in even with careless alignment, and sometimes it won't stop digging in no matter what you try. Take note if the first part in a similar batch broaches easy, they all do. If it goes south, they all do. Something is different between these tough and easy batches, and it is not alignment.

Stone the hook of the broach on the cutting surface on every tooth. Not the top pushing end of the broach. Just reduce the rake angle a bit with a land a few thousandths wide. It takes a few minutes of careful work. It does not ruin the broach. I do not advocate reducing the front clearance with a stone. That does ruin the broach.

Most things will broach ok, but the many responses show broaching trouble is not uncommon. It's always the same, big at the bottom. Even with perfect alignment if the back rake, or hook, of the broach is too high the broach will hog in at the bottom, leaving a tapered keyway at best.

If alignment is the primary cause of the broach hogging, why is the keyway  never big at the top? Doesn't poor alignment go both ways?

Reducing the hook angle of a broach is not a cure for poor alignment, a worn out press, or poor procedure. Firstly everything should be square and the ram motion should be perpendicular to the platen. Once all this is confirmed and the broach still hogs the only thing left is excessive hook for the material.

Imagine a broach with an absurdly high hook. It's easy to see how it will dig in to the work and move away from the bushing. Now slowly reduce the hook and the broach will dig in less. Eventually you will reach a hook angle where the broach will not dig in at all. Proceed to a negative hook and the broach will be pushed away from the cut. Since different materials have different cutting properties, it makes sense this maximum hook angle to prevent hogging will vary with material.

To produce a general purpose tool the broach manufacturer chooses a hook angle for general purpose, not every purpose. Nobody disputes a drill will self-feed if the rake angle is too high for the material. The solution is to struggle with the drill and maybe make a good part, or reduce the rake angle for an immediate cure.

The same goes for a keyway push broach. Just try it and you will be amazed how easy the rest of the job is, and how nice the parts are.
 
THANKS for all the great responses and info guys!! Appreciate it!

Though now you've got me paranoid about "hogging in"!

Vettepilot
 
Though now you've got me paranoid about "hogging in"!

Vettepilot,
I haven't read all the posts, but there is a simple, effective way to prevent hogging in. I have experienced this problem and figured out why it happens. There is no need to modify the teeth.

If you have a collared bush, don't push it all the way into your hub. It needs to stick out above the top of the hub more than sticks out the bottom. I do this by putting a spacer under the collar, on the top side of the workpiece. For example, I used slotted clamp in the photo. It needs to be something that will clear the broach teeth.

The Dumont catalogue says to put the collar underneath the workpiece. This would be good if you can do it, however I usually find it doesn't suit the base of my arbor press.

I broach lots of small sprockets and timing pulleys and the keyways always come out parallel using the above method.

If you have plenty of power e.g. a hydraulic press, then you can disregard the above and broach both hubs at the same time (i.e. stacked on the bush) and the keyways will come out parallel. Depends on your hub length of course.

Regarding pressure to cut a 1/4" keyway - Dumont say 2580 lbs required for the maximum length of cut (2 1/2"). So if you hub is say 1" thick, and your broach is new, your 1 ton arbor press will be fine.

Lube the backside of the broach as well as the entire cutting length. I use black cutting oil.

However, if your hubs are cast iron, you wouldn't normally use cutting oil (but lubricate the back of the broach).

Re. making a bush....I have made a special size bush, but wouldn't recommend it. You have to mill an accurate deep, narrow, slot with parallel sides....I would buy a bush if it is a standard size. Besides, aluminium is not really an engineering material :D

Hopefully you have bought a decent broach (probably C/111 size) which will be just under 12" long. I have seen imported broach sets which are much shorter/smaller and I don't like the look of them.

I do quite a lot of broaching on my arbor press, not sure what tonnage it is. Maybe 1-2 tons. It handles 8mm (5/16") OK. A new broach makes a big difference. I do 4, 5, 6 & 8mm keyways in sprockets and timing pulleys. The good thing is that it is fast. Much faster than a hand-pumped hydraulic press, but requires a good arm muscle. My press is locally made, fabricated from steel and machined for a good fit, not one of those horrible, sloppy, cast iron import jobs.

Broaching 4mm with Whakatiki Engineering Arbor press 02 edit.jpg Broaching 4mm with Whakatiki Engineering Arbor press 03 red.jpg Broaching 4mm with Whakatiki Engineering Arbor press 01 edit.jpg


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I was recently surprised to find Dumont and Hassay-Savage now have the same owner (Pilot Precision Products). :skep::scratchchin:
 
Thanks again guys. I guess when the broach arrives, I'll give it a go.

Note: I really gave serious thought to "pecking it" in the mill, but then decided to order a broach instead. If I break the broach, I WILL be "pecking" it...
:~(

Vettepilot
 








 
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