Dmt 450 runout and Chuck removal

[wcndave]

I noticed that I was getting a lot of chattering and did some quick tests discovered I have about 0.3mm run out on the tip of my centre point.

It is a sorby Chuck.

My first thought was to remove chuck, clean the threads and put it back on, however I cannot get it off by hand. There are opposing holes on the drive shaft, however I have no tool that will fit this.

Any ideas



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[wcndave]

Actually closer to 3mm !

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[wcndave]

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[finneyb]

Try opening chuck jaws and closing them on a large screwdriver to act a lever
Insert allen key or similar in shaft hole and turn to lock allen key against lathe body - shaft is now locked.
Apply gentle but firm pressure to screwdriver

HTH

Brian

 

[wcndave]

I did try putting Allen key in the hole, but not with screwdriver in jaws. Apply pressure to screwdriver, you mean turn it?

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[CHJ]

A short sharp tap with a wooden or hide mallet on the chuck lever with the spindle locked will probably be more effective than steady pressure.

Is the chuck body running out? if not then it is more likely that the scroll/Jaw carriers and accessory jaws are the problem causing run out, rather than the chuck to spindle joint if it's never been disturbed.

On the chatter/vibration front, it may be that the spindle bearings are giving up.
To check, place dial indicator on chuck body and provide leverage to the chuck body with a length of wood lodged in the lathe bed.

 

[paulm]

Looks like you have a stebcentre mounted in the chuck jaws ?

It's very easy to have this run off centre, you need to ensure the flats on the stebcentre (assuming it is the type designed for mounting in chuck jaws, rather than that with a morse taper) are in contact with the inside faces of the jaws, and it may take a couple of attempts to achieve this and make it run true.

Could also be that you have the chuck jaws mounted out of sequence in the chuck, if you have had them out to clean it or change jaws recently ? In this event you should see the outside of the jaws run out of true ?

Cheers, Paul

 

[wcndave]

Try opening chuck jaws and closing them on a large screwdriver to act a lever
Insert allen key or similar in shaft hole and turn to lock allen key against lathe body - shaft is now locked.
Apply gentle but firm pressure to screwdriver

Okay, brain fart. I didn't want to do this because I was worried about damaging the jaws, but I see what you mean now. The problem is that the shaft hole that you see in the picture is only a quarter of an inch deep, so putting anything in it to lock the spindle just doesn't work.

A short sharp tap with a wooden or hide mallet on the chuck lever with the spindle locked will probably be more effective than steady pressure.

what is the chuck lever? the problem with this is that I simply cannot lock the spindle.

Is the chuck body running out? if not then it is more likely that the scroll/Jaw carriers and accessory jaws are the problem causing run out, rather than the chuck to spindle joint if it's never been disturbed.

I do get run out on the chuck body as well, however not sure whether the tolerances for the body are the same as the jaws.

On the chatter/vibration front, it may be that the spindle bearings are giving up.
To check, place dial indicator on chuck body and provide leverage to the chuck body with a length of wood lodged in the lathe bed.

The part of the spindle that I can see appears to be running true, however hard to tell.

What is the purpose of providing leverage with a length of wood?

Looks like you have a stebcentre mounted in the chuck jaws ?

It's very easy to have this run off centre, you need to ensure the flats on the stebcentre (assuming it is the type designed for mounting in chuck jaws, rather than that with a morse taper) are in contact with the inside faces of the jaws, and it may take a couple of attempts to achieve this and make it run true.

the stebcentre does have flat and rounded parts. I have been putting the rounded parts against the jaws, given that the inside faces of the jaws are themselves round. Is this not correct?

I have also tried quite a few attempts at repositioning and rotating the stebcentre to no avail. I can clearly see that there is run out on the jaws of the chuck.

Could also be that you have the chuck jaws mounted out of sequence in the chuck, if you have had them out to clean it or change jaws recently ? In this event you should see the outside of the jaws run out of true ?

When I received the jaws they were not marked as being in a particular sequence.

When I am doing turning, I take them out four or five times a session, as I switch between 4 inch and 1 inch jaws.

Thanks already for the good advice, it seems the problem of removing the chuck is the fact that I cannot lock the spindle, there may be a special tool for this, but I can't find it.

I'm going to cross my fingers that the problem of the run out is related to the sequence of the jaws, only 24 permutations to try!

Here is what I have been making for interest.

 

[Mark Hancock]

The problem is that the shaft hole that you see in the picture is only a quarter of an inch deep, so putting anything in it to lock the spindle just doesn't work.
.

You need to get a bar that is the diameter of the shaft hole and long enough so that the other end rest against the bed bars. This will lock the spindle whilst you use tap the lever as suggested through the jaws of the chuck.

Mark

 

[Doofusme]

I have the same lathe and have a bar approximately 5" long that fits the spindle holes, I usually bring up my tool rest to hold it against and then a sharp push on the screwdriver in the chuck technique gets the chuck loose.
Do you also use a washer between spindle and chuck? i was advised about this as the spindle thread is long and can be longer than the thread in the chuck which can cause tightness problems !

Hope that helps.

Phil

 

[wcndave]

Ok, I will give it another go.

It seems that the spindle hold is shallow, and rounded, so whatever I put in there just twisted out, but if it works for you, then it must be possible ;-)

Putting a washer in would seem to make the problem of long spindle worse no? I did have an issue with this, and got a friend who works for a machining company to increase the depth slightly which sorted it.

Thanks

Dave

 

[Doofusme]

"Putting a washer in would seem to make the problem of long spindle worse no?"

No, the washer goes over the spindle thread to prevent the chuck screwing back against the un-threaded shoulder of the spindle.

 

[CHJ]

What you really need to hold the spindle is an appropriate C-Spanner.

By chuck lever I was referring to anything you have clamped across the chuck jaws as a lever.

 

[wcndave]

So after bending two steel bars that were in the little hole to lock spindle and gripping a large crowbar in jaws it came loose. Thanks guys!

Closing jaws to maximum extent reveals an imperfect circle in the middle, so having them in right position may do the trick... family time now so I will have to live in suspense a bit longer...

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[Mark Hancock]

So after bending two steel bars that were in the little hole to lock spindle and gripping a large crowbar in jaws it came loose. Thanks guys!

Closing jaws to maximum extent reveals an imperfect circle in the middle, so having them in right position may do the trick... family time now so I will have to live in suspense a bit longer...

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Closing the jaws completely will give an imperfect circle because it's the optimum position for the jaws to hold that gives a circle. This is usually where the outer edge of the jaws are in line with the body of the chuck though it does depend on the make of chuck and jaw design.
Perhaps Chas can do a drawing to explain this better

 

[CHJ]

Due to how the jaws are manufactured*, they only form a true circle at one point, usually with a 3-4 mm gap between the jaw segments.

* They are machined on a lathe to form a true circle then cut into segments with a milling cutter which removes material from the disc.

This gap of course in real life has an advantage that small amounts of debris won't affect the setting of the jaws at a true circle in an inward direction and also accommodates for a holding socket that is less than ideal on the minimum size.

A mis-fitted jaw carrier will throw the jaws out by more than the width of the manufacturing 'slot'

 

[wcndave]

Thanks chas, so my intended method was to try different combinations with the stub chuck in until it was true.

Is it correct that the order of jaws could be my run out problem? I hope so in many ways as it's easily remedied and anything else could be way more serious.

Also when I take the chuck off, i get knocking sound, which i don't with chuck on. Symptom of bearings going? The spindle is perfectly true, i put a morse centre in and there was < 0.01mm run out.

Thanks again
Dave

 

[Spindle]

Hi

I don't have a patriot chuck but the following is generally the case for all scroll chucks:

The chuck body will have the jaw locations identified - usually numbered from 1 to 4

The chuck jaws will be likewise identified 1 to 4

The jaw adaptors will also be identified 1 to 4 - the jaw adaptors are the four metal turnings attached to the jaws with two screws each.

To confirm the correct assembly of the chuck:

Remove the jaw adaptors and wind the jaws all of the way out of the body.

Locate the #1 jaw in the #1 housing on the chuck body and whilst squeezing the jaw towards the centre of the chuck with your thumb, turn the jaw chuck key in the expand direction until the jaw clicks and moves toward the centre. This click indicates that you have located the begining of the scroll thread.

Now turn the chck key slowly in the contracting direction and the jaw will begin to move inwards. Dont turn the key any more than half a turn.

Now insert the jaw marked #2 into the #2 housing and continue turning the chuck key until the #2 jaw begins to move inwards.

Repeat for jaws #3 and #4 - the jaws will now be correctly positioned in the body. Check by fully closing the jaws - they should all meet when fully closed and should grip something suitable, (a drill for example), concentrically.

Assemble the jaw adaptors to the jaws matching their respective identifying numbers.

The chuck should now be correctly assembled and concentric.

If you still have run out problems it sounds like it could be the chuck not registering on the spindle thread correctly.

Regards Mick

 

[wcndave]

Thanks for that.

I have never removed the jaws, I guess I am using wrong terminology. The toolpost site lists them as "jaws", but all I am removing are the two threaded screws and swapping between jaws (adaptors).

I bought two sets of jaws with the sorby chuck, and they came separately boxed, so there was never any respective identifying numbers, and they cannot have been matched to fit - that's what has me unsure as to whether this is the issue.

Sounds like I just need to try it!

 

[chipmunk]

Hi Dave,
When you replace the jaw screws are you making sure that the jaws are concentric before tightening then down fully?

The best way I know of doing this is to just tighten all the screws up enough so that the jaws are just held but not so tight that they do not move about and then tighten up the chuck with the key so that the jaws come together and align themselves. Then tighten all of the jaw screws down fully. Otherwise there's a distinct possibility that the jaws will be out of line.

HTH
Jon