Workpiece movement.

[ukracer]

I have a Colchester Master 2500 and its done a few projects over the past year or so since I had it but .......every so often while taking a reasonable cut it seems as if the work piece rides up. Trying to see where the play comes from is awkward.

I had it happen today but upon checking the work piece was loose in the chuck. I then did a few tests and it does seem as if there is a bit of play even if the work piece is tight. I am not sure if this is coming from a bell mouthed chuck or the bearings.

It will take a 1mm cut ok but anything over that and it thinks about riding up over the cutter.

What should I look for first...

 

[Spark plug]

What diameter is the workpiece, how far from the chuck are you cutting.

Is the tool in good condition, is the tool height ok.

 

[ukracer]

What diameter is the workpiece, how far from the chuck are you cutting.

Is the tool in good condition, is the tool height ok.

Appreciate all of that mate and I just turned up 4 posts fairly reasonable. But I would not have expected that sort of visible upwards movement if I push the cut hard.

 

[brightspark]

tool height has a fair bit to do with it and pushing the cut in hard . simlar to parting off and the job rides up over the tool if the lathe saddle and cross slides are worn the tool will be pulled down lower than the center height and dig in. try locking the saddle if your just facing off . if the chuck spindle bearings are worn put a large bar in the chuck and give it a pull and check for wear

 

[Spark plug]

Appreciate all of that mate and I just turned up 4 posts fairly reasonable. But I would not have expected that sort of visible upwards movement if I push the cut hard.

The biggest cause of upward movement of the workpice is tool height set too low. This may not make a big difference with larger diameter material but smaller material will try to climb up the tool as its cutting.

What material are you cutting and what type of tool?

 

[Kent]

Besides all said (which is all possible) have you checked each jaw is of the same type (its not unknown for one to be mixed in from another chuck in the past) and often they are numbered in relation to the chuck 1 - 1 , 2-2 etc.
Its one of those things that need checking that's all along with tool height and wear

 

[ukracer]

Besides all said (which is all possible) have you checked each jaw is of the same type (its not unknown for one to be mixed in from another chuck in the past) and often they are numbered in relation to the chuck 1 - 1 , 2-2 etc.
Its one of those things that need checking that's all along with tool height and wear

Its not the workpiece moving as it turns accurately after it sits down again.

 

[ukracer]

The biggest cause of upward movement of the workpice is tool height set too low. This may not make a big difference with larger diameter material but smaller material will try to climb up the tool as its cutting.

What material are you cutting and what type of tool?

This one. And its mild steel i am turning. just some old rod I had lying about.

This one does the same.

Not tried any more cutters recently BUT I dont usually take big cuts as I come from a Raglan 5 inch lathe I have thought I saw the work piece rise up before. I thought I was imaging it then. Now I know I have seen it lol

It really does seem like the chuck rises so it could be main bearing . this is what worries me.

 

[brightspark]

View attachment 47124

This one. And its mild steel i am turning. just some old rod I had lying about.

This one does the same.

View attachment 47125
Not tried any more cutters recently BUT I dont usually take big cuts as I come from a Raglan 5 inch lathe I have thought I saw the work piece rise up before. I thought I was imaging it then. Now I know I have seen it lol

It really does seem like the chuck rises so it could be main bearing . this is what worries me.

or the toolpost pulling down. put a dti gauge on the headstock on to the chuck run it slow and take a cut u will soon see if its flexing or moving

 

[ukracer]

or the toolpost pulling down. put a dti gauge on the headstock on to the chuck run it slow and take a cut u will soon see if its flexing or moving

Yeah I was just about to test it today when the heavens opened and I had to get everything back inside quickly lol

 

[brightspark]

speed and feed will play a big part. using tip tools or any other type .also the length of overhang out of the chuck if it ist centered and held with the tailstock center .it could be any number of things

 

[MattF]

Just hoick on the various pieces and see if there's movement, (when it's not running, obviously). There's either slop somewhere else it's likely tool bit or height related, as suggested.

 

[ukracer]

Just hoick on the various pieces and see if there's movement, (when it's not running, obviously). There's either slop somewhere else it's likely tool bit or height related, as suggested.

Ok update on this. It was as I thought a bell mouthed chuck. I used a piece of pipe (4 inch) to allow me to bore it out by tightening on the outside of the jaws. Whist it worked and its a lot better now but I did not go mad as I was not sure how true the pipe is. I turned up a piece of real tat. approx 5/8th in diameter and to be honest its passable.

BUT I tested with a piece of 8mm ali and you can see the results here.

The end of the bar is just out of the chuck. The rest of the rod is up the mandrel of the lathe.here should be 4 marks on the ali bar but there is only 2.

 

[Wallace]

That looks like the jaws are worn. Is it on all 3 sets?

 

[ukracer]

That looks like the jaws are worn. Is it on all 3 sets?

Yes..But I did try and tidy them up and the work piece does not move visibly now.

https://www.facebook.com/video.php?v=10152666251503400

 

[Wedg1e]

or the toolpost pulling down. put a dti gauge on the headstock on to the chuck run it slow and take a cut u will soon see if its flexing or moving

I had this on my Student: it turned out to be the whole top slide moving on its base! Some muppet had used loads of threadlock when screwing the two halves together and the surplus threadlock had gone into the gap between the two castings, meaning that with sufficient force the top half could deflect (or tilt) towards the rear of the lathe.
Drilled out the screws, scraped off the threadlock, put it back together properly, no more problems

 

[Wallace]

Yes..But I did try and tidy them up and the work piece does not move visibly now.

Are they soft jaws?

 

[ukracer]

Are they soft jaws?

Thats what I am wondering. They certainly cut with a carbide tipped boring bar although I took very very small cuts in case.

 

[MrFluffy]

True-ing up jaws back to parallel and concentricity is the one job that real toolpost grinders are made for if you have one/can borrow one. The better the grinder, the better the result.
You need to load them with a jig which applies pressure but still lets the grindstone pass all the way through. Theres a downloadable jaw jig you can make from logan, but last time I just drilled and tapped the jaws axially and bolted a ring inside the holes, but that chuck was destined for the bin anyway it was so worn (it rattled the jaws when rotating when it wasnt clamping a workpiece).

I'm going to buy a new good chuck soon, I know everyone and his dog can work round worn out chucks and its some kind of lathe badge of honor, but I'm personally sick of having to do so.

 

[MrFluffy]

The ring you used to true your jaws up wont work as well by the way, as its loading the jaws in the wrong way relative to the surface you are truing up. So any play in the jaw ways and the accuracy will be compromised and they will rock the wrong way. Hence the jig just above.