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Toothe broke on lathe chuck

Tooth broke on lathe chuck

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Jeremy Smith 224/05/2020 08:06:53
88 forum posts
15 photos

280a87eb-fc2b-4cea-a650-ab6dfb14d620.jpege5093b8e-57ae-4b1a-8605-3aeb6ce89bd3.jpegToday when i was tightening down my lathe chuck on the myford10, one of the splines snapped off. Can this be salvaged ( ie can i remove a spline off of the other teeth to make this work again)?

Edited By Jeremy Smith 2 on 24/05/2020 08:07:57

Edited By Jeremy Smith 2 on 24/05/2020 08:08:40

Michael Gilligan24/05/2020 08:22:14
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20190 forum posts
1053 photos

Ouch !!

Not certain about this Jeremy, but I think you could continue using it un-modified

Just change the ‘timing’ of how you insert the jaws

.

it looks like #3 will need to be inserted one-full-turn late

MichaelG. 

Edited By Michael Gilligan on 24/05/2020 08:27:27

Tony Pratt 124/05/2020 08:35:32
1966 forum posts
12 photos

Michael is correct just carry on & use the jaws.

Tony

DC31k24/05/2020 08:36:40
686 forum posts
2 photos

It may not be a good idea to remove anything from the other jaws.

As Michael says, one small issue is the timing of jaw insertion. If you have the means to drill the hardened jaw, you could insert a pin in the middle of the broken tooth location just to help timing.

You will need to look at the scroll to see how many teeth it engages in normal use. If it is only two teeth, then perhaps avoid using the chuck at diameters where one of the engaged teeth is the missing one.

John Haine24/05/2020 08:50:23
4679 forum posts
273 photos

I think you should look carefully at the scroll to see if there's a reason why it snapped. Were you in the process of fitting the jaws, or tightening it on a bar? If the latter, were the jaws near the outer end of their travel so most of the load was on the spline that snapped? If so then the other jaws would have had more splines engaged to take the load. But I agree that provided you can get the timing right (which shouldn't be too hard, just insert jaw 3 one turn of the scroll late), and you don't try to use the chuck on material that's tool big, it should be fine.

Mick B124/05/2020 08:50:31
2192 forum posts
122 photos
Posted by Tony Pratt 1 on 24/05/2020 08:35:32:

Michael is correct just carry on & use the jaws.

Tony

I think that's right too. My Myford Speed 10 chuck was like that when I got it - presumably it happened when somebody chucked a workpiece on the absolute upper size limit, then tightened severely.

Apart from having to change the insertion sequence, and accepting a lower limit on worksize, I was able to use that chuck as was for the 15 years I had the lathe. I pointed it out to the subsequent buyer and it didn't bother him either.

Harry Wilkes24/05/2020 09:03:05
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1344 forum posts
65 photos

I too the same problem on No2 jaw and when I have to reinstall it I have to insert it on the second time round of the scroll.

H

Gavlar24/05/2020 09:12:05
102 forum posts
4 photos

I have a drawer full of assorted Burnerd chuck jaws. I got them as part of a job lot and they don't fit anything I currently own. If your chuck is a Burnerd and you send me precise dimensions of your broken jaw, I can't promise to have the right ones but I'll have a sift through to see if I have a suitable set.

J Hancock24/05/2020 09:12:56
836 forum posts

Usually caused by overtightening/shock load when at the extreme capacity of the chuck.

Martin Connelly24/05/2020 10:47:15
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2137 forum posts
222 photos

I think I would find out at what position it was furthest out with two teeth still engaged with the scroll and permanently mark it with a maximum usable position there. The risk of holding something large with only one tooth held by the scroll strikes me as risky. There are good reasons for having both inside and outside jaws for a lathe.

Martin C

Alan Hopwood24/05/2020 10:57:10
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40 forum posts

Why not just phone Rotagrip, quote the number of the chuck and price up a replacement set of jaws. The hardened ones will be pricey, but get a quote on a soft jaw set and machine them to suit.

Alan.

Clive Foster24/05/2020 13:55:51
3135 forum posts
109 photos

If you still have the broken tooth consider cleaning the surfaces up properly and glueing it back in place with a strong cyranoacrylate adhesive. Maybe one of the flexy variety would be better. I'll not pretend 100% success but "I'll glue it for now to see this job out and fix it properly later when I have time." repairs have sometimes done well enough that later never came.

When it comes to chuck jaw projection beyond the body I was taught never go beyond the first step from outside in.

Which is probably more like three teeth engaged than two. Many of the better quality chucks have marks on the jaw to delineate maximum extension. The ones I have are in close agreement to the one step rule.

Some smaller chucks have rather skinny scrolls so best to check and, if need be, modify your maximum extension rule accordingly.

The scroll on the inexpensive, but unreasonably accurate for the money, Chinese 5C spigot mounted one I have is a good example of the skinny scroll. I got it with a 5C Spindexer for milling duties where a lesser grip is than required for turning is generally acceptable so not a major worry there. However my lathe has a 5C native spindle "taper" so it does get used on turning duties with the jaw projection rule tightened to less than half a step out maximum.

Clive

old mart24/05/2020 14:41:46
3775 forum posts
233 photos

J Hancock has it in a nutshell. It pays to compare the teeth overlap while the jaws are out of the chuck, you really need three teeth minimum engaged when the jaws are at maximum opening.

Martin Connelly24/05/2020 16:37:13
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2137 forum posts
222 photos

Clive, I have not heard of the one step rule before so I went and had a look at my usual 6" 3 jaw chuck. The scroll usually has 4 lands showing in the slot with 5 where the start and finish overlap. Positioning both inside and outside jaws over the scroll with 3 teeth engaged matched the one step rule perfectly. My other 6" chuck has soft jaws mounted on it so no way to apply the one step rule there. I did remove the jaws to see where the jaws would engage with the scroll with about 1/3 of the length protruding and it was 2 teeth but this is because over most of the scroll there are only 2 lands on the scroll with 3 where start and finish overlap. They are much chunkier than the other chuck so probably have similar strength from 2 teeth engaged as the other with 3 teeth engaged.

Martin C

John Haine24/05/2020 16:43:34
4679 forum posts
273 photos

Of course the best way to avoid this problem is not to bite your chuck in the first place.....

I'll get my coat...

Philip Burley24/05/2020 16:53:00
avatar
198 forum posts
1 photos

I have one like that , the first "ridge" on nunber one jaw was only just hanging on and broke off early on I just have to remember to load up 2, 3 then ! ,

Phik

Jeremy Smith 225/05/2020 03:11:47
88 forum posts
15 photos
Posted by J Hancock on 24/05/2020 09:12:56:

Usually caused by overtightening/shock load when at the extreme capacity of the chuck.

Bingo!!!!!!

i figured that out once it happened. I have been trying to time it accordingly so i could still use them, but have been unsuccessful.

Jeremy Smith 225/05/2020 03:16:51
88 forum posts
15 photos
Posted by Gavlar on 24/05/2020 09:12:05:

I have a drawer full of assorted Burnerd chuck jaws. I got them as part of a job lot and they don't fit anything I currently own. If your chuck is a Burnerd and you send me precise dimensions of your broken jaw, I can't promise to have the right ones but I'll have a sift through to see if I have a suitable set.

Which dimensions will you need from me? I would really appreciate this.

Jeremy Smith 225/05/2020 03:20:49
88 forum posts
15 photos

How should i be loading these into the chuck? I’m stumped on which sequence to do it in...tried a few times.

Gavlar25/05/2020 06:35:10
102 forum posts
4 photos
Posted by Jeremy Smith 2 on 25/05/2020 03:16:51:
Posted by Gavlar on 24/05/2020 09:12:05:

I have a drawer full of assorted Burnerd chuck jaws. I got them as part of a job lot and they don't fit anything I currently own. If your chuck is a Burnerd and you send me precise dimensions of your broken jaw, I can't promise to have the right ones but I'll have a sift through to see if I have a suitable set.

Which dimensions will you need from me? I would really appreciate this.

I'll message you

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