Thread: Cross-slide play

Hi All,
I tried out my CTC brand carbide-tipped boring bars today. I've never tried boring before and the first thing that struck me was how much the bar deflected as the cut progressed. I initially suspected the bar was flexing, but on closer inspection I could see that the cross slide was actually rotating to the right.

After locking the carriage I grabbed the rear of the cross slide and tried moving it from side to side. There was what seemed (to me) to be a lot of sideways play (I wasn't expecting any). See the photo for clarification of where the play is. Imagine the arrows are curved- the cross slide seems to pivot around the front.

Should there be any movement in this direction? Is this a gib adjustment issue?

Chris

Yea the gib need adjusting... A bastard of a job with that design of gib.

But you will get flex regardless if you take too heavy a cut.... I have a 260 as well and while a good lathe for it's weight, it is still only a lightweight lathe...

Originally Posted by .RC.

Yea the gib need adjusting... A bastard of a job with that design of gib.

I'm guessing its just a flat gib, not a tapered one? I have the same issues with mine, i am seriously thinking about machining the slide to take a tapered gib.
Ewan

How old and worn is the lathe. Any movement here is an indication of wear or poor adjustment. Try adjusting the jib a bit at a time while moving the cross slide thru its full range of movement.

My lathe is old and worn and if I adjust the jib with the cross slide near the rear of its travel it is too tight when I bring it back to the front. There should be minimum movement.

Let us know how the boring bars go as I am in the process of locating bits for my holders etc so I know where to get stuff when I need to. CTC is a name I am interested in.

Dean

Looking at what you have described dosent appear to be very clear,at least to me.
Which way were you feeding?
If you were feeding towards the chuck the feeding load would be towards the chuck side of the cross slide,it would of been pushing the cross slide onto the dovetail.
If the cross slide is rotating to the right I would suggest to put a feeler in to see what clearance you have.
I take it that after seeing this movement that you have allready adjusted the screws on to the gib.How much movement do you now have after adjusting and taking another cut.
How free and easy was the cross slide to move before you started boring?
What results have you noticed when turning outside diameters,at a guess it would seem that your cut would deepen when turning OD's.

Originally Posted by jack620

Hi All,
I tried out my CTC brand carbide-tipped boring bars today.

Can you confirm what sort of bars you got?

If boring, the tool may want to move out of the cut (this is another problem entirely, and it really depends on what bars you have) and rotate the cross slide and compound clockwise, so the back of the slide should have gone to the right. Is that correct?
Does the 260 have 1 or 2 locking screws on the gib?

Ewan

Ok, here's some info I should have provided in my first post :

The lathe is a late model Hercus 260 (ex high-school). The cross-feed nut is quite worn (0.8mm front-to-rear play), so I guess the cross-slide has seen a bit of use.

I was only cutting Delrin (acetyl).

These are the boring bars I'm using:
9 PCS. 1/2" BORING BARS WITH CARBIDE TIPS #G14

Now, to answer some of your questions:

I was feeding towards the chuck.

I haven't attempted to adjust the gibs yet. I wanted to determine where the problem lay before I started messing around with adjustments.

I haven't noticed any movement when turing ODs, but then wouldn't the force in this case be trying to rotate the cross slide to the left (or does the tool pull towards the workpiece)? Also, the cross slide is further to the rear when boring than when turning, which might account for any difference in movement.

Perhaps I could try raising/lowering the boring bar holder by adding/removing shims? Then I would have to rotate the boring bar in the holder to return the tip to centre height. This would decrease/increase the angle the cutting surface makes with the workpiece.

Regardless of any of the above, there is quite a lot of movement in the cross-slide which I would like to eliminate.

Originally Posted by Ueee

....so the back of the slide should have gone to the right. Is that correct?

Does the 260 have 1 or 2 locking screws on the gib?

Ewan,
yes, the back of the slide moves right.

I think there are 3 gib-screws in the 260's cross slide. I'll go and check then get back to you.

Chris

Did you resharpen the tips to suit what you were cutting.
The cross slide may move towards the left if facing,if turning od I would hope the feeding force was pushing towards rear.
You not going to do any harm in adjusting the gib,its only 4 or 5 srews with locknuts.

hi

I've never had any success using those carbide tipped boring bars in my Sheraton 9 lathe , it just doesn't seem to be rigid enough to handle the forces . Or, maybe it's me doing something wrong again

HSS boring bars are so much easier to use in lathe of that size , for me anyway .

With the back gear in, and about 80rpm, and a slow feed . I can do 4 - 5 mm boring cuts with ease with my chipbreaker HSS boring bar .

From what I have read, carbide needs a very rigid setup

Mike

I hate to say it but those bars ar not really up to much, especially in plastics. You would be better of with a bar that takes hss. you need some top rake and a sharper lead angle to help the tool want to stay in the cut, rather than push out of it. If a tool is pushing out of a cut then it has more to do with the tool shape than the lathe itself (up to a point anyway)
Thats my experience anyway, there may be other forumites with better suggestions.
As for the gib locks, i mean that, locks not adjustment screws.

Ewan

Originally Posted by morrisman

With the back gear in, and about 80rpm, and a slow feed . I can do 4 - 5 mm boring cuts with ease with my chipbreaker HSS boring bar .

Mmmm, I was using 1250RPM. I've always turned Delrin at very high RPM. Should I slow it down for boring?

Ewan,
sorry, I thought you meant gib adjusting screws (it's got 5). I don't think the 260 has a cross slide gib lock. Can anyone help here?

I do have a bar that takes HSS but it's too big for the hole I want to bore. Bummer about these bars not being much good for lathe work. Oh well, they only cost about $30 delivered.

Originally Posted by pipeclay

Did you resharpen the tips to suit what you were cutting.

You not going to do any harm in adjusting the gib,its only 4 or 5 srews with locknuts.

No PC, I just opened the box and got stuck in. I've just dragged out my copy of Fitting and Machining (RMIT) which has a lot of info on boring tools. I should have read that first.

I'll adjust the gib screws tomorrow before proceeding any further.

Chris

I have 2 Seco carbide tipped boring bars, a 12mm and a 16mm. I have no problems with these in my lathe except that I take lights cuts because my lathe has a lot of play. They may have better angle settings than the ones Chris is using. They use triangle tips and both cut to an internal shoulder. I set them about 1mm above centre and cut towards the front of the lathe.

When turning OD the cross slide would be pushed clockwise. Buy some boring bars and suddenly the force is working the other way. I cut and ground a partoff end on some 1/4 inch HSS recently to fit in my HSS holder. Tried to part off 25mm diam with 16mm bore MS. Worked ok for about 3/4 of the depth then grabbed and broke off, bending the work slightly. I had machined it without taking it out to get ID and OD concentric. Wasn't that important but I did it for practice. Forget about parting for now. In excess of 2mm play in the cross slide screw / nut. Sigh.

Dean

Here's the tool setup, in case anyone is still confused.