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Problem broaching keyway

TheOldHokie

Aluminum
Joined
Apr 28, 2005
Location
Myersville, Maryland
Hi all,

I'm having a problem broaching a simple 3/16" square keyway (1.25" LOC) in the 5/8" bore of a hub I made. I don't do this often and in the past I've had no problem. But this last time I can't keep the broach from running too deep on the backside of hub. It's like the cutting action of the broach is pulling the broach into the hub and away from the guide bushing. I didn't have the proper size (B) broach and purchased an inexpensive import and I'm wondering if perhaps the cutting angle on the teeth is ground wrong. My other broaches are all Dumont and I've had no problem with them. Or is this a setup/execution problem?

TOH
 
Well, you could inspect the tool you bought.

Is this another case of...The AMERICAN TOOL COST TO MUCH and I CAN SAVE 30 Cents so I bought the CHINEEE CRAP?
 
Gary,

No - this is a case of the American tool cost $50 and the Chinese crap cost $20 and I need two keyways in a part for which I'm getting paid $50.

Thanks for the help.

TOH
 
My other broaches are all Dumont and I've had no problem with them. Or is this a setup/execution problem?
Yeah, it's an exicution problem. Instead of buying a tool that would work hundreds of times and could last you 10 years, you buy one that wont even do the job on the first part.

What YOU get for your work is not Dumonts problem.
 
rather than putting you down for trying to make the best of a situation let me ask this.

are you cutting this in one pass or two as normal using the shim behind the broach?

also is your guide a good fit and are you supporting the part solidly?

are you doing this in an arbor press?

i had a similiar problem a couple years ago and my boss was too hyper and wouldnt listen to me about the proper tooling, simple guide, we only messed up 6 out of 10 pcs. :D ...jim
 
Gary,

It's assholes like you that come out spouting flame instead of reasonable advice that have ruined too many Internet forums. If I was a professional doing this for a living I'd likely invest in that quality tool. But I'm a hobbyist doing a few favors for friends basically for the cost of materials and the simple enjoyment of learning a little bit about an interesting trade. Apparently your mentoring skills are limited to rude exhortations to BUY AMERICAN. I don't frequent this forum and quite frankly if this is the kind of exchange I can expect I won't be back.

Thanks for the tip,

TOH
 
Jim,

Thanks for the gracious reply.

1) Two passes and the broach runs out badly on both.

2) I can tell no difference in the fit between the import and the Dumont broaches.

3) The part is solidly supported on two 3/4" press plates in a hydraulic press. The hub is made from 12L14 so it cuts quite easily.

I found the problem after the first pass with the new broach. I recut the keyway 180* out from the first attempt and by stopping every tooth or so and re-aligning the broach I was able to produce an acceptable keyway. As I said I'm a rank amatuer and I thought I'd asked for some advice from more experienced metal workers.

Thanks agian,

TOH
 
TOH, I think it may be a problem with the rake angle.

There should be some form of "back pressure" so to speak from the cutting action that pushes the broach back against the guide bushing slot.

However, I don't really recommend trying to modify it...that could *really* screw things up.

Sounds like you got it done with the realignment bit.
 
You can justify any and all of what ever you want, but it boils down to the fact that you expected to get a good tool just like the one you have had NO PROBLEMS WITH...(your words, not mine) for CHEAP... you reap what you sew, some day your customer will do it to you when they tell you they gave the order to a elCheapo guy.
Then you you claim to be "I'm a rank amatuer" ..wich is it, a guy that has no problems ever with Dumont or a amatuer cant be both?
 
TOH,
Please don't let GaryE be a turnoff, he's our resident extremist on the Buy American issue. I fully understand your dilemma as I am retired and only use my shop equipment part-time, trying to recoup some of the overhead and satisfy the IRS requirements to write some things off from my taxes on my retirement income! There are times when I also have to balance the cost and usage frequency into a tool purchase decision.
In fact, I am considering a keyway broach set purchase from Enco now and the import is so much cheaper I may have to give it a shot!
If your setup is good and sturdy, you are using arbor press and everything is straight and square, it should cut OK. I have broached many keyways when all I had was a hydraulic press, what a PITA,LOL.
If you continue to have trouble, take a good close look under a glass at the side profile of the teeth on the broack. They may have too much positive rake and are actually pulling the broach into the cut.
If this proves to be the problem, you should be able to carefully reduce the rake from the front of each tooth with a Dremel stone or similar. I suggest finding a piece of scrap of a similar material to your part and drill some holes in it to broach till you find and fix the problem, rather than spoil the part.
Dave
On edit: Looks like I typed too slow! Glad you made out OK.
 
Matt,

Thanks. Your analysis is pretty much what I suspected but I've done so few keyways I wasn't sure I hadn't just lucked into the proper technique previously. If I get a chance I'll compare the rake angle on one of the Dumont broaches to the import and see if I can discern any difference.

TOH
 
TOH
I have had the same problem in the past both with broaching & having to buy cheap tools.
As for the broach if there is a lot of play in the press it will move off center, what I have done with some success is to put a shim under the part to compensate for the broach moving inward on the hub
this forces the tool to move the other way also stop & push the broach up so you can re align it.

On the subjet of cheap tools some times you can't afford the nice expensive tool as much as it would be better you have to make due with what you have.Been there & have all the scrap to prove it!!

Jackmo
 
We've also encountered this problem when the bushing you're using is much longer than the part you are broaching. When broaching smaller gears/sprockets, we always use a dummy part with the same size bore on the bottom which keeps the bushing and broach in contact until it clears the bottom (dummy) part.
Side note, we only broach a few hundred smaller parts a year and as our Dumont set has worn out or we need to buy a metric broach, there has never been a problem with the imports cutting properly. Even on bushings which we have to make, such as when a customer wants an bastard size keyway in a standard bore. (3/16" keyway in a 1" bore for example.)
 
We've also encountered this problem when the bushing you're using is much longer than the part you are broaching. When broaching smaller gears/sprockets, we always use a dummy part with the same size bore on the bottom which keeps the bushing and broach in contact until it clears the bottom (dummy) part.
Txangus, That makes a whole bunch of sense. I haven't run into this issue as TOH but your analysis makes good sense. Thanks. I'll file that away.
 
TOH:
Next time try an alternative approach. Rather than buy a keyway braoch when i have one or two keys to make i simply slot them in teh mill. Setup the Bport with a tool like a boring bat that had a revoviable tool bit. Sharpen a piece of HSS to the width of the key with a small positieve front clearance. Position the part on teh table with parallels under to allow tool clearance on the back side. Use the hand quill feed to push the tool through the part. as a vertical shaper. Raise the tool , feed the table a amall amount and repeat the vertical stroke...continue until the key is to depth. With this method you can make any size key you need and it won't cost anything..just a bit of time.
Cheers Ross
 
I have done alot of parts quill shaping like AlfaGTA, and also using the carrage of the lathe for the movement. I like the carrage on the lathe better. Just remember the cross slide dial reads 1/2 actual travel.

You can quill shape a tapered keyway that would be tough on a lathe.
 
Ill tell you what to try and usually it works.Lay a dowel pin on top of the broach so it lays perpendicular to the cutting teeth.This will allow the broach to straighten itself up and not kick as its pulled in.Try it. Jim
 
Hello,

This can be a common problem in 12L14 material with good American broaches. I found that adjusting the broach back in the guide bushing as you go helps. Make sure the setup is pressing the broach straight down at all times. Sometimes pushing on the broach towards the front or back will also help. Good luck ! Come back to visit the forum again.

Brian
 








 
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