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Keyway Broaching

Using a tailstock?

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FullaFlava15/12/2019 16:52:01
30 forum posts
52 photos

To fit a power feed I’ve had for ages to my mill, I have a need to increase the diameter of the bore of the drive gear and then make a 5mm keyway. The keyway will need to have a length of approx 70mm and the material is brass.

I’ve never used a keyway broach before and am unsure how much force is required. Do you think ill be able to push one through with the tail stock on my HLV clone?


Joseph Noci 115/12/2019 17:01:08
593 forum posts
859 photos

I have broached quite a few bosses in aluminium, none as long as 70mm, and it takes a surprising amount of force. I would be reluctant to put that sort of force on the tailstock screw. Also, that load transfers into the tailstock body and lathe bed. I assume you have all the stepwise increment wedges for the broach as well. Whatever method you end up using, ensure that the force on the broad is really square-on and inline - a 5mm broach bends easily! Also, remove and clean out the chips regularly - 70mm is a long way to go!


JasonB15/12/2019 17:02:54
17257 forum posts
1858 photos
1 articles

Better to try with the mill's quill or even a drill press though a hydraulic press is preferable.. Though it is a long keyway and you will have a lot of teeth engaged that will take quite a bit of effort and may well clog the gullets of the teeth so you might have to withdraw the broach part way through to clear out the chips.

David George 115/12/2019 17:10:27
1094 forum posts
353 photos

You can cut an internal keyway with a square tool in a boring bar. you make a cutting tool like a part off tool just the width of the key you need and then wind the tool forward without moving the spindle taking small cuts perhaps only a few thou at a time till the depth required. it is better if you can cut a groove in the bore previous to cutting the keyway as it gives you something to run into. if you can lock the spindle is good, at least put it in back gear and isolate the motor before starting.


FullaFlava15/12/2019 17:31:35
30 forum posts
52 photos

Thanks for that, I have planed keyways as David described before but was hoping a broach might be easier, which it likely is with the proper tools.

Im not sure I have enough headroom in the throat of my mill to use the quill, perhaps I could get over the edge of the table provided I can hold the job properly.

Mike Poole15/12/2019 18:16:10
2414 forum posts
53 photos

You will need a guide bush as long as the hole you wish to broach or you will snap the broach.


HOWARDT15/12/2019 18:19:38
504 forum posts
14 photos

Can you shorten the key slot as 70 mm is long and a normal broach may not bee able to produce a size slot that length. Looking at the shaft the key could be recut further down. The norm is to create a relief diameter to clear the slot depth just beyond the key seat. Alternative is to create a separate keyed bush and retain it with screws into the longer bush. Just a thought on alternatives.

Brian Oldford15/12/2019 21:02:02
598 forum posts
4 photos

Can you get access to a shaper? They are one of those much undervalued machines well suited to such tasks.

Hopper16/12/2019 04:34:46
4110 forum posts
89 photos

Machine tools such as lathes and mills are not presses, which is what you need to force a broach through metal. Don't even try it. You risk damaging your tailstock or mill. Find someone with a hydraulic press or make up something with two lengths of fine threaded rod of stout diameter and two stout steel plates, one to hold the job in place, the other to bear on the broach.

Paul Lousick16/12/2019 05:20:05
1306 forum posts
520 photos

I broke a small drill press trying to broach a 3mm keyway. So proceed with caution.


Robert Atkinson 216/12/2019 07:22:53
540 forum posts
21 photos

A small arbour (arbor?) press is not expensive and a better tool for the job than the lathe or mill. Once you have one you will find it useful for all sorts of jobs. a 1/2 ton one from china starts at about £35 shipped on ebay, with 1 ton "shipped from UK" at under £50.

Robert G8RPI.

JasonB16/12/2019 07:41:54
17257 forum posts
1858 photos
1 articles

I think you would need at least a 3 ton arbor press to get the height, without going down to the workshop to measure my 3/16" broach is 7-8" long and add to that the 70mm part and you want close to 300mm height to play with. You won't even get the broach into a 1/2ton one!

Ron Laden16/12/2019 07:54:05
1694 forum posts
306 photos

There is a pre owned 3 ton arbor press on Ebay at the moment £80 which has 300mm of travel.

FullaFlava16/12/2019 08:16:27
30 forum posts
52 photos

Many thanks for the replies and opinions, much as a press seems a good idea, I don’t see a use for one beyond this job (plus having to put it somewhere) and I thought the lathe might be a work around.

A buddy 35 miles away has a 10 tonne hydraulic press, if I get all the shizzle required together, I’ll go and borrow the use of it.

From what I understand, I’ll need the broach, the gear, a full length 70mm steel bushing with a slot, shims which I suppose will also need to be full length and lube.

I’ll also look at the shorter bush as mentioned by Howard T, but I’m not sure there’s enough meat on the diameter to have an insert and be strong enough.

Alistair Robertson 116/12/2019 09:49:40
77 forum posts
6 photos

A push broach will work fine but care is really needed. When we had long bore to keyway we usually made up a sacrificial bush (of the same material!) then drill a hole of the right size through the assembly. This removed most of the material leaving the broach to square things up.

The length of the broach will be the problem and need an extension so what we did was grind the top end of the broach to a diameter then machine the extension piece to fit on to it. This meant everything was in line and we didn't have to juggle and hold bits with a hand under the press ram!

I once broached a steam engine pulley that was about 9 inches long with a 1/2" keyway through an 2 1/8" bore with no problems.

not done it yet16/12/2019 10:16:06
4122 forum posts
15 photos

I don’t have a clue about this power feed device. I just see a pic of a shaft and a part which needs to fit together.

First, which way does that piece fit over the shaft?

How much do you need to enlarge that hole? Doesn't look like a lot.

Perhaps these people giving info on broaching do know of this particular power feed, but personally I would not want to be broaching through that length of material with that width of broach unless the broach was quite a ’deep’ one. I have the facility to press a broach, but have always found an alternative approach ... so far.

Howard and Brian, above, offer sensible alternatives, one of which I would adopt. But even if using my hand shaper, I would relieve as much of the unnecessary section before starting to cut.

Nicholas Farr16/12/2019 11:08:14
2107 forum posts
1017 photos

Hi, I wouldn't think a 5mm Broach wouldn't take too much to push through, however I've never done it in brass and it may be prudent to do more passes than normal by using thinner shims, which are easy enough to make, thinner shims may help stop the Broach digging into the brass, but as I say I've no experience of broaching brass.

Below is a photo I did through a steel pulley 1" thick with a 1/8" Broach with my No. 4 flypress, which was no bother at all.


Headroom is the thing, both my 1/8" and 3/16" Broach's are 6 3/4" long to give you an idea, but the effective height is about 6" above anything I need to broach because they will sit into the bore about 3/4" before the fist cutting edge starts to touch.

Regards Nick.

Hopper16/12/2019 11:10:03
4110 forum posts
89 photos

Could you even do away with the rather inconvenient long keyway and use instead a dowel pin through the gear and shaft? Make it out of brass and it could be a safety shear pin?

JasonB16/12/2019 11:19:30
17257 forum posts
1858 photos
1 articles

The other way to ease the load is to push a smaller width broach through first, I have done this several times when I could not be bothered to make the trip to my friend with the hydraulic press, just shim the smaller one so it cuts to the same depth as the larger. Doing it this way I have done 40-50mm long keyways 3/16" wide in cast iron flywheel hubs with just the old Naerok drill press to push them through with.

If on the lathe then using teh carrage to plane the keyway would be my preference to the tailstock but turn a runout groove part way down teh bore then you only need do about 25mm length. These four 3/16" wide ones on the left are all 1" long and in steel just planed with the carrage.

Similar can be done on the mill using it like a slotter, quicker if you have a quill than just a knee.

Michael Gilligan16/12/2019 11:21:42
14920 forum posts
638 photos
Posted by Hopper on 16/12/2019 11:10:03:

Could you even do away with the rather inconvenient long keyway and use instead a dowel pin through the gear and shaft? Make it out of brass and it could be a safety shear pin?



Now that’s what I call Engineering yes


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