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Clunky broach

Is this normal? It sounds ghastly!

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Robin12/03/2022 15:38:34
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551 forum posts

I got 2 horizontal arbours with my mill and the 22mm is missing a keyway.

I am cutting a 6mm keyway in to Chinesium steel spacers and part ways through it starts to go clunk every time a new tooth starts.

Doesn't seem to do this for experienced keyway cutters on YouTube so it must be me.

What am I doing wrong? I tried so hard, this is jolly unfair sad

Never posted a movie on here before, will this work?

https://www.youtube.com/watch?v=ia1ppsRFPFU

 

Edited By Robin on 12/03/2022 15:46:00

Edited By JasonB on 12/03/2022 16:08:19

Robin12/03/2022 15:47:53
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551 forum posts

I am not doing at all well here. I can't change it to 450mm wide, much too late for that. You will have to use your fertile imaginations sad

Edited By Robin on 12/03/2022 15:58:47

JasonB12/03/2022 16:08:00
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Is the broach guide bush almost as long as your spacer if not that won't help. Other problem as it's quite a long keyway is that the gullets of the broach may be getting full, pull it out to clear then and press in again.

Re the video. On Youtube click share, then click Embed and copy the long code. Then when posting click the youtube icon and paste that code. It will just show a box with "Iframe" in it until you submit the post

Edited By JasonB on 12/03/2022 16:10:20

Brian Wood12/03/2022 16:22:42
2566 forum posts
39 photos

Robin,

Are you trying to cut the keyway in one pass in a guide that is machined to the combined finished depth of the broach and keyway you are trying to cut?

The guide depth should be deeper so that the broach can cut a keyway to part depth, then a slip is inserted behind the broach to allow the broach a second pass and cut deeper and a second slip put in behind the broach to complete the cut to depth. There are guides on how it should be done and forcing it through hydraulically could even fracture the broach..

Done in stages as I have outlined, the teeth on the broach are able to shave the keyway to depth progressively without loading them too highly

Regards Brian

Edited By Brian Wood on 12/03/2022 16:25:08

JasonB12/03/2022 16:35:12
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Oh just heard you say the broach guide is 15mm deep. should be about the same as the spacer otherwise the broach deflects away from the cut.

DiogenesII12/03/2022 16:37:11
559 forum posts
221 photos

Did you test how tough / hard the spacers are first..?

..some (a lot) of Asian 'precision' tooling bit's and pieces can be bloody tough..

Shortening even a cheapy boring bar can cost a hacksaw blade..

Alistair Robertson 112/03/2022 16:52:40
145 forum posts
6 photos

The guide should be about the same length as from the last cutting edge to the end of the broach or at least the length of the material with a minimum of 3 cutting edges in the work.

A powered hydraulic press is best as the speed of the stroke is consistent. A hand pump is not the best.

We used these broaches in production work and we "lifed" them for 1000 units but they would do much more than that with no problems if properly lubricated with "broaching oil" the name of which escapes me now!

Robin12/03/2022 17:28:29
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551 forum posts

The guide was slightly longer than the part, but it was also slightly too big for the hole in the table so I had to cut it flush. I am cutting in two passes using the backing piece that came with the broach. It has the correct length. The cuttings are on the chunky side, I will try clearing them halfway through...

Is there any way this could be normal? I am a novice broacher.

Ady112/03/2022 18:19:17
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5089 forum posts
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A total guess from watching your video

It sounds to me like you have taken a slightly too-big bite... and then it pops free

That high up the broach you are also deep into the cut so the edge is cutting/grabbing more as well as the tip

like parting off, additional stresses appear the deeper you go in so relief angles which were fine at the start become more critical and less effective

Edited By Ady1 on 12/03/2022 18:23:11

not done it yet12/03/2022 19:57:24
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Would I be adding a keyway to a horizontal arbor? I don’t think so. The arbor is likely to finish - err- not quite straight. Can’t help with the spacer problem, apart from suggesting they are left alone.

The 1” arbor on my Centec mill doesn’t have a keyway, so I never bothered with the smaller arbors I made.

David-Clark 112/03/2022 20:36:37
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I think you are trying to cut it too much at a time.

Start with a little shim and gradually open it out a couple of thou at a time until it is about full depth.

I used horizontal mills and never used keys on the actual cutter. Many old arbors ysee will have groves in them where the slitting saws have spun. Just make sure the collars are tightly clamped.

If the cutter keeps spinning use a collar with a key in it next to the cutter but between the cutter and the arbor, never in the actual cutter.

JasonB12/03/2022 20:47:04
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You are supposed to start with no shim *, then add the next. Typical Marlco at that size is 5 passes. No shim, 3 passes each adding a 0.75 shim and final with the three 0.75 and one 0.5 shim in place.

* Some smaller width ones do need to start with one or two of the shims, makers data should say. example

Some cheaper broaches take off more per pass and need less shims but they are thicker so if you have one like that it's likely you have a coarser pitch cut so it won't be as easy as a fine pitch one. Compare one from the ME suppliers and that only uses one shim at 6mm so you are making the cut in two passes not 5 so expect the effort to be at least double.

There is a reason the Marlco are called LITEcutwink

Edited By JasonB on 12/03/2022 20:56:18

David-Clark 112/03/2022 20:52:02
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Yes, Jasonb, sounds about right. It does depend on the size of the key and the material you are broaching.,

Robin13/03/2022 00:16:45
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551 forum posts

The broach goes from 15mm to 16.65mm in one pass. The shim is 1.65mm thick so this broach must be that cheapo, coarse cut jobbie you describe. The tooth form dictating the shim.

Curiously it has 22 teeth so I expected 0.075mm / tooth, but the chips are over 0.4mm thick and nowhere near the 60mm length of the cut. Part cut, part crunch it would seem.

Anyway, the keyways are cut, the job is done, the broach survived. I have some aluminium to cut next, that has to be easier. Doesn't it?

I can't see that slotting the arbour would cause significant bending. I put a 15x10mm trench in the broach guide and that seemed to stay straight. A longer 6x3mm groove is nothing. Is it? thinking

Pete.13/03/2022 01:35:59
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801 forum posts
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Have your 'Chinesium' spacers been hardened? sorry to insult your intelligence but sometimes the simple things are overlooked.

Hopper13/03/2022 11:50:53
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And never run a key in a slitting saw. They can explode if a tooth digs in or jams. You'll only ever do it once, guaranteed.

Baz13/03/2022 12:23:23
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I was always taught that cutters under 1/4 inch wide you keyed the arbor and collars either side of the cutter but not the cutter itself, for cutters wider than 1/4 inch you keyed the cutter. Totally agree about slitting saws exploding, have seen dozens of them, I would also say that you should not use power feed with slitting saws for the same reason.

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