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Broach Bushings?

Vettepilot

Plastic
Joined
May 9, 2020
Hi,
Hope this thread isn't too old to jump in, and please don't laugh at me...

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
 
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I like to plunge an on-size endmill down edge of the bore as deep as I can. Then the broach really only has to clean out the corners.

It also helps if the keyway has to be timed to other features.
 
IMO an aluminum bushing would work fine for your use. You're not doing a production job. You'll lube things up anyway so you'd be hard pressed to measure any wear. I don't know without looking it up, but I suspect the broach will be designed to cut full depth in more than one pass, add a shim or two to get full depth. You can check the difference in height between the first and last tooth to see how much it removes in one pass. Shims can be shim stock, or even fudged from what you have handy if you have to make up full thickness. I don't know on arbor press vs hydraulic. It might be an issue of how much head room you need.
 
Consider buying a bushing for the broach you have. The broach will be marked A,B or C. Or I, II, or III, etc. Appropriate bushing will come with shims to cut to proper depth.
 
Hi,
Hope this thread isn't too old to jump in, and please don't laugh at me...

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 require more height and tonnage than a 1 ton arbor press. An aluminum bushing will be adequate for limited use. Make the slot just deep enough for the small end of the broach. Use a good, thick lube like STP.
 
Be aware that keystock that's supposed to be a particular dimension, like 1/4 inch or 3/16 can actually be oversize by three to five thousanths of an inch. For some reason the plated keystock that is sold as "Precision" brand is maddeningly oversized, sometimes by .005. So be sure and mic your keystock. I don't know what the average person does when they buy this brand, which is sold by MSC and J and L. I've ground quite a bit of it, until I gave up and found other brands of keystock that are on size. I guess they make it assuming you're replacing key stock in wallowed out keyways.

I use to wonder why all my prints had keys cut with woodruff key cutters, but it's for the reason Forrest stated. You Don't get an onsize keyseat cut with an on size mill.
The plated stuff is maintenance stock. Try 1018 sq stock from your steel supplier.
It is tough to one shot small ones in a Bridgeport but you can one shot keys with stub end mills. A #4 KT Vertical does this easily.
 
Hi,
Hope this thread isn't too old to jump in, and please don't laugh at me...

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
Alignment of the broach bushing and hub are paramount. Your bushing should have a squaring shoulder to facilitate this. A 3/8” broach takes as I recall 3 passes. The first is bare and then w/ 1/16” shim then w/ two 1/16” shims Good luck
 
I forgot to mention, when broaching, orient the broach so you can see the profile of the teeth. This will allow you to see if it is digging in (off perpendicular) before it's too late. If it does dig in, push the BUSHING out (not the broach), remove the broach, turn the part over and start again from the opposite side.
 
I forgot to mention, when broaching, orient the broach so you can see the profile of the teeth. This will allow you to see if it is digging in (off perpendicular) before it's too late. If it does dig in, push the BUSHING out (not the broach), remove the broach, turn the part over and start again from the opposite side.
Sometimes the broaches really hog in, and quickly. If reversing as above doesn't cure the problem modify the broach. The back rake angle is designed to suit common needs, but won't work for everything. Slightly reduce the back rake angle on all the teeth with a stone. This will cure the hogging in. The broach won't cut as free on some jobs, but it will still cut.
 
Sometimes the broaches really hog in, and quickly. If reversing as above doesn't cure the problem modify the broach. The back rake angle is designed to suit common needs, but won't work for everything. Slightly reduce the back rake angle on all the teeth with a stone. This will cure the hogging in. The broach won't cut as free on some jobs, but it will still cut.
I will dub a drill bit for a cause but I will not ruin a broach because I am not paying attention to alignment until it’s too late.
 
I will dub a drill bit for a cause but I will not ruin a broach because I am not paying attention to alignment until it’s too late.
I actually called Dumont about a batch of parts that just couldn't be broached without hogging in. Dumont reccomended altering the back rake with a stone, saying sometimes this was a necessary modification.

This doesn't ruin the broach at all. It can still be used for other jobs. And it's not a matter of ignoring alignment in any way. Sometimes material and/or length of cut will cause the broach to hog in no matter what you do or how careful you are. Believe me been there done that! Like many of us have.

I did work for an old guy thay would take a crummy stone and bash, and I mean bash, away at the front clearance to prevent hogging in. This definately does ruin the broach and doesn't work for shit.
 
A very gentle tilt opposite way from the gauge when starting can prevent hogging in. Also you must come off contact pressure often during stroke to facilitate alignment of the pressure to the part/bush/broach.
 
A very gentle tilt opposite way from the gauge when starting can prevent hogging in. Also you must come off contact pressure often during stroke to facilitate alignment of the pressure to the part/bush/broach.
Yes Sir, backing off is very important. My old KR Wilson elec. powered press is so slow, backing off seems annoying but needed.
 
Much of the reason the broach digs in is pushing at the wrong spot on the broach. Push as close as possible to directly above the teeth, even if you have to grind the top of the broach at an angle. If you push on the heel of the broach the force vector direction is for the broach to dig in.
 
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.
I've never found any way to hold the broach parallel to the bore. There just isn't any. Being careful does help, but the broach will broach where it wants to broach.

Some guys make an extended bushing way above the top of the part to keep the broach from "tilting". It maybe helps a bit but the broaching problem is still there. The "tilting" is the result of the broach hogging in. More top support just puts a flimsy bandaid on the real cause.

Think about a broach hogging in some cases the same way you think about a drill self-feeding in some soft materials. You can try to hold the drill back and struggle and maybe get through a part. Or mayne ruin it. But the drill is just doing what is in its nature because the rake angle is too high for the material. Stone a slight reduction on the rake angle and all the struggling ends.

It is much the same with a push broach except worse because the length of cut variable is added to the material variable. It just takes a tiny land on each tooth. And just like the stoned drill, the stoned broach still works for other materials, just maybe not as free cutting.

When the Dumont guy told me this I wasn't happy, but I tried it and it worked great. Give it a try.

I also think as long as a 1Ton press has a tall enough throat it will work. We had a job every once in a while that was a 1/4" keyway about 3" long in 4140 pre-hard. 1.5 Ton press bolted to the wall with a cheater pipe would do it. Nobody liked to see that job come along, and a little guy couldn't do it. You really had to pull/jerk until your feet got real light to get just a little movement. But the broach lasted quite awhile. That broach didn't hog in.:D
 
It is simple enough to make a cap for the end of an arbor press spindle that would hold the broach in good alignment, but not something I'd do unless I was doing a ton of broaching. The pin trick that concentrates the force directly above the broach teeth that I described in the linked thread - and additionally, if necessary - reversal of the part on subsequent passes has always worked for me. Altering the rake I would do as long as I had a spare broach. Or I'd order a new one after I did and keep the altered one for troublesome parts like brass.
 
My question is about stand practice when cutting keyways. I know I can make it work, but I want to make it standard, if possible.

Key stock is square. So, using 1/8" key as an example and cutting a keyway in a shaft and a gear, what is the point of reference for the depth of the keyways on the shaft and on the hole in the gear? Seems to me that it would almost have to be at the center of the keyway on the surface of the shaft or hole. But I would like this confirmed.

If this is correct, where and how much additional allowance should be provided to allow easy assembly and interchangability?

Also, how much allowance is normally provided on the width of the keyways?
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.
 








 
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