Ahhh - Frustration - Box of bits - Jaws...

Recently the new owner of an old Harrison 140 lathe (@1972).

Having spent sometime now cleaning, repainting and generally making good 40 years of use (from what I can tell only slight use) I took my first few cuts, and all is well and I am extremely happy with it ---- BUT, as there's always a BUT -- I have a very small annoying problem.

I have turned a few test pieces over the past few weeks and was confident to try my first real go at making something I needed, modify a 2.5MOD spur gear to fit in my Herbert Mill table gearbox.

All was going well having first faced it to depth - bored it to the spindle size and even cutting in a key way. I then had to turn the piece around to reduce the boss of the gear by 2mm - this is where my annoyance started.

When I purchased the lathe it came with boxes of bits and pieces and in amongst the bits where outside jaws for my chuck, i remembered picking them up from under all the none useful parts and muttering to myself "Oh that's good at least Ive got those" I promptly cleaned them and gave them a good rub with a very oily rag and put them away for an occasion at which I would need them - the occasion had arrived, sooner than I would have imagined but now was the time to change my chuck jaws to help me hold the spur gear - I am anticipating everyones thoughts at this point - and yes you are correct - they are not the right jaws.

Or should I say, they are the right jaws, well 2 of them are the 3rd is also a 3, if you get my jist. I have a 1 and two 3's, obviously they don't work with the chuck so my spur gear had to be held very strangely in my internal jaws - still managed to do it with a few thou to spare .....

Looking through a well know auction site there are plenty of jaw sets for sale at the moment but nothing that I can see that are the same dimensions as my chuck - 8" Pratt Burnard -

I read that its not a good idea to use chuck jaws that weren't supplied with the actual chuck at purchase, I can only think this is down to them being ground to suit the chuck.

If I do manage to find a set of jaws the right dimensions what would be the pros/cons or is it just all Cons......

Obviously if anyone has a set of jaws that would suit then please let me know.

NB - I'm a beginner - reference to doing things wrongly as mentioned above is my learning curve.

Edited bit - If anyone has a 1 and two 2's I know where your 3rd one is !

Edited By Me. on 05/02/2021 14:53:39

Rotagrip might have something

Pheeeewwww - Thanks, but I think I would prefer to buy a good used chuck with extra jaws than spend that sort of money on a set of jaws.

I hadn't actually looked specifically, Me. , but I'd bought this for £25 some time ago and was happy with it. .

Soft Scroll Jaws To Suit Pratt Burnerd 4" Dia Chuck:

Edited By Peter Greene on 05/02/2021 15:23:31

Thanks - I'd like to stick with my 8 inch job. I'm sure something will turn up.

Are reducing the bos in diameter or length?

If length, it will not matter too much, if the cut on the face is slightly eccentric. What will be important will be to ensure that both faces are parallel. As long as the out of parallel is not excesIive, and is less than the installed clearance, it may not be absolutely correct but will do the job..

If you are worried about concentricity, as you should be, if you cannot hold the gear in a 4 Jaw and clock the bore to get it concentric, you could use the 3 jaw to make a collet for the gear, using the jaws that you do have. It will, have to be a "Top Hat" type of collet, with the smaller section (Preferably as large a diameter as possible ) and then without disturbing anything bore the larger (outer ) section to take the gear.

Mark the collet in line with Jaw 1, remove and split axially (away from the mark for Jaw 1 ).

Refit to the chuck with the mark against Jaw 1, insert the gear, and tighten the jaws. The gear should then be acceptably concentric and ready for further machining. Very probably more concentric than if you had all 3 external jaws for the chuck

PS,

Hopefully the two jaws that DO relate to your chuck will carry the same number, and hopefully a number which is the same as the chuck, so that you know which to use when you find a .replacement.

Any chance that inserting Jaws 1 and 2 in the correct order, and engaging 3 either before or after 3 you might end up with an useable set up? As desperation stakes, it may be that playing musical chairs with the 3 jaws relative to the jaw slots (Keeping 1 and 2 in sequence ) an acceptable situation might be found. If this did work, you might want to remark the external jaws to match the slots in the body giving the desired result. If you can get to about 0.005" or so you're away!

HTH

Howard

That is a good idea I will try to insert the jaw at a different place on the spiral maybe it will get almost there and then I could - regrind the jaws !!!! - or is that owned upon.

I did note that when the jaws were going in it did tighten up as they got closer to the middle like something was binding.

Me.,

You have a private message.

John

Knowing that somewhere in the workshop were sets of spare jaws, went to find them, to see if there would be any of use to you..

Frustratingly, there are 5 new sets of hard INTERNAL jaws for Pratt Bernard 160 mm chucks, (2210-17603 )but No EXTERNAL!

Sorry!

Howard

First try out the jaws in the chuck body. Then measure the one that fits carefully and make a note of the teeth pitch. There are a huge number of chuck jaws out there, but very few vendors have any idea of how to measure them and often quote the serial numbers mistakenly thinking they are part numbers. Genuine jaws may cost more than the price of a complete chuck and then there is no telling how worn your chuck body is.

If you have milling or grinding machinery, you could modify a jaw to match them up. The error is 1/3 of the scroll pitch.

Can You post basic dimensions?

it's a long shot, but do the jaws have any punch or grind marks that might change the numbering?

Hi All - thanks for the replies

1. I have finished my Spur gear modification

2. I have tried the jaws (external) I have in my chuck and they are nice a smooth apart from the last inch towards the centre.

3. Yes they have part numbers on - I will post what they are later

4. I will post dimensions

5. No - the chuck or the jaws have not been tampered with.

I will post more info tomorrow.

Thanks

Come to think of it that is the number stamped on mine - I think - do you have magic wand that could reverse the jaws....

If your chuck is imperial, it will have a scroll pitch of 1/3", so a no3 jaw in a no2 slot will be 0.111" too deep. If the chuck has a metric scroll, pitch 8mm, then no3 jaw in no2 slot will be 2.66mm too deep.

Yeah ... sorry about that. This thread was riding tandem with one about the ML7 chuck in the listings and I had a bit of a senior moment.

Info - for those interested in my dilemma -

I have 3 jaws - 2 of them have 32617 both stamped 3. these don't fit very well and are a little tight. I have tried these in the 3 position on the chuck and also in the 1 and 2 position.

I have another stamped 42542 stamped 2 and is a nice fit and runs nice and smooth.

The chuck has "Pratt Type No 358L" label on it.

All 3 jaws are the same dimensions.

I am considering

1- a new chcuk

2 - a set of jaws to fit my chuck

3 - a different hobby

4 - the will to live longer than my next project.

You might consider a new chuck. Finding jaws for a 40+ year old chuck would be a challenge. If you do purchase aa new chuck consider one with 2 piece jaws. The top jaws are reversible so they will always be on the chuck. It also allows the use of soft top jaws for special jobs.

Good luck.