Author Topic: Lathe Chuck Backstop  (Read 8841 times)

Bogstandard

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Lathe Chuck Backstop
« on: September 15, 2012, 06:31:09 PM »
How many times have you had to make a load of bits on the lathe all to the same length.

PITA isn't it?

What you need is to push the bar back into the chuck until it comes to a dead stop, then once tightened, you can use one setting to cut the face, and every one after that will be the same length, within a thou or so.

So this is how I went about making my chuck backstop.

This is about one of the cheapest but best bits of kit you can make for your lathe, and if used correctly can save you hours of machining time, and reduce recycling to zero.


First off, I got a soft end blank morse taper to fit my machine, theses are only a few squid each and I usually have a couple in stock of the two sizes my lathe uses, just in case a job like this comes along. If you want to go the cheapskate and difficult way, and make your own, that is up to you. To me, for the cost of them, they are just not worth making.
The normal sizes used for lathe spindles nowadays is either 2 or 3 morse taper.

http://www.arceurotrade.co.uk/Catalogue/Blank-End-Arbors



The soft end needs to be reduced so that it will fit thru the smallest centre of your chuck range into the spindle without having to remove the chuck. The easy way is just to reduce it down to where it meets the taper.




With the chuck off the machine, mount it into the spindle nose.




Turn down the soft end until it is the same size as the largest part of the taper. As you can see, it will now easily go into the smallest part of my chuck, the centre hole in a 5C collet.




Drill down the centre as far as you can go with a tapping drill of your choice. I am using an 8mm thread, for a 2MT I would suggest 6mm or 1/4" thread.
You will most probably find you can only drill down the length of the softened end, which will give you about 3/4" adjustment on the stop length.




Then tap down as far as you can go.




I used an 8mm coachbolt, but you could use almost anything, even threaded rod if you have it. Screw it as far in as it will go, and tighten up the locknut.




I have removed the chuck jaws to show you what is going on.
All power off the machine, stick a rag into the spindle end and push it all the way thru the spindle with a stick. You do this every time you fit anything into the morse taper in the nose, just to get rid of debris in there that will stop the MT seating properly.
Feed the backstop thru the chuck and get it seated in the spindle.




This is bit of a hoptical dillusion. You need to mark up the screw length just before it would hit the back of the jaws. So if the jaws are tightened up, they won't touch the backstop screw.




Cut the screw to marked length, and face it off.



This shows how the screw fits, it isn't screwed all the way in just so I could get this angled shot. Normally you would take the stop out when not in use, and when you fit it, you adjust it to length to push your part back to, ensuring the locknut has been tightened before mounting it into the spindle..



As mine is, it can only be used with parts that are larger than 8mm and longer than about 25mm (1"), that is because it isn't completely finished.
I will put say a 4mm (5/32") thread in the very end of the 8mm adjusting screw, and make up little adapter noses for smaller material sizes. Just as I have done for the 5C collet backstop in the top of the picture. You soon end up with all sorts of ends that you keep in a little box for almost any occasion.
The bolt at the bottom could be faced off and used for a backstop for material having a hole thru it, say a bored cylinder. You just have to use your imagination a bit.



If you don't understand anything, just ask.

I can't give any machine specific answers, because unless it is the same as mine, I just won't know. But ask away anyway, because someone on here will know what you are talking about.



John


Online Jo

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Re: Lathe Chuck Backstop
« Reply #1 on: September 15, 2012, 06:48:39 PM »
Magic :ThumbsUp:, thanks John.

I will make one of these rather than a 5C backstop.

Jo
Usus est optimum magister

Offline Don1966

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Re: Lathe Chuck Backstop
« Reply #2 on: September 16, 2012, 01:01:55 AM »
Thanks John I need to make one.

Don

Offline sshire

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Re: Lathe Chuck Backstop
« Reply #3 on: September 16, 2012, 02:41:35 AM »
John
Thank you very much. You cannot believe the schemes I had devised when you mentioned a spindle stop. This is brilliantly elegant. As soon as I finish this post, I'm ordering a few blank morse tapers for my spindle. It had not occurred to me that the standard 5c collet stops would give differing lengths depending on tightness of the chuck key and part diameter. But of course it would!
Thank you again
Stan
Best,
Stan

Bogstandard

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Re: Lathe Chuck Backstop
« Reply #4 on: September 16, 2012, 07:02:42 AM »
Stan,

If you want to be really frugal about making one, you could use the MT ends of old large drills, they are usually only hardened from just below the flutes forwards.

For smaller lathes, this type of stop isn't usually a very viable proposition, as the centres of small chucks don't allow the stop to be fitted and removed through them, and so the chuck usually has to be removed to fit it. OK if you have a lot of items to do, but not really viable for just one or two.

John

Bogstandard

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Re: Lathe Chuck Backstop
« Reply #5 on: September 16, 2012, 08:44:17 AM »
Just as a little update to the above statement where small lathes are concerned.

This is an idea that may be of use to someone who can't load a stop through the chuck.

The front support would need to be before the taper starts in the spindle, and I am sure that an easy to make taper lock could be designed and made to lock the stop into the spindle. This was just a quickie idea, and I am sure that someone has already made something along these lines that might even be simpler.

John