Keep snapping centre drills

I wonder if any of you knowledgable folk can shine a light on my problem.

I am a newbie, having recently acquired a restored ML7 ,and want to teach myself how to use it. I have been reading books, watching youtube and practicing to try and find my way.

I want to drill a centre hole and using a centre/countersink drill in a Jacobs chuck, the moment it contacts the work it wobbles, describing an arc as though not straight. Keep advancing and the misalignment snaps the tool!! I feel the tailstock needs aligning. The locking lever can lock it in a different position if I slacken it, physically push the tailstock over, then lock it again, since there's play in the bed if not locked in position. Presumably this is normal?

I feel I am missing something embarassingly simple...

it sounds like it's off centre. To check. Put a centre in the headstock or turn a taper point on some scrap metal in the chuck. Put a centre in the tailstock and offer this up to the taper just turned. The points should meet.

The tailstock should not move sideways so this could be that a shim in missalined or even missing.

I'm not familiar with your machine but there should be some sideways adjustment on the base of the tailstock to adjust the centre.

Once you have the two centres roughly but fairly closely alined then try centre drilling again on a length of soft bar Aluminium would do. Do the same to the other end. Then between centres take light cuts and see how parallel the bar is once cleand up. If it's narrow at the tailstock end adjust it slightly away from you. If its large at the tailstock then adjust towrds you. When parallel the tailstock should drill centrally. Hope this helps.

The tailstock can move sideways when not locked. There's a block underneath with two alen keys to adjust it against the lathe ways. Is this what needs adjusting?

Sounds like the tailstock is set over off centre by a mm or two , i think on the ML7 the adjusting screws are on the bottom of the tailstock near the back should be allen type grub screws, a quick way of setting it fairly accurately is to face a piece a bar in the chuck and leave a very small pip then put a dead centre in the tailstock and bring the point up to the pip , lock up the tailstock and adjust the left and right hand screws until the pip and dead centre points line up , that should be good enough to centre drill , i am assuming the jacobs chuck will hold the centre drill pretty true as they can be a bit out sometimes , turning them through 180 degrees can sometimes help there and if it does mark it so you can put it in the same orientation each time , to turn a length parallel between centres or chuck and centre you will need a clock (DTI) to fine tune the tailstock alighnment which can sometimes be a tricky task for even an experienced hand.

Edited By Kettrinboy on 28/12/2015 20:26:25

probably yes. That will be a gib strip. Just pinch it up until you can slide the tailstock without lateral movement. Not too tight or you will wear the slides. Then check the alignment with either the taper or pip as Kettrinboy suggested.

Also check for bumps or burrs on the mortice taper in the tailstock and drill chuck. be sure they are clean or the chuck could twist. Also try ketrinboy's idead of turning the chuck 180 degrees.

if you do adjust the tailstock only move it very small amounts using the grub screws. Loosen one side then tighten the other. Only about an eigth of a turn maximum.

Once you are happy with the alignment try shortening the centre drill. I always grind mine back before using them.

Quick and accurate way to check alignment. Put centres in the headstock and tailstock, bring them up to face each-other, then trap a 6 inch steel rule between them by gently feeding the T/S forward, trying to trap the rule right at its centre. The rule should be at right angles to the lathe axis however it's rotated.

Also there may be too much play between the T/S barrel and the bore it slides in.

Hi
I agree with Chris shorten the center drill . toolmakers do it all the time

Nobby

Kit,

Please get yourself a proper Myford hand book for your lathe as it will tell you exactly how to adjust the tailstock.

PDF copies can be downloaded free or Myford will sell you a copy.

Thanks for the help guys, I have the handbook anyway.

Have you faced off the bar completely flat with no raised pip at the centre?the tool must be at the centre height,the smallest pip will deflect the centre drill point ,as a beginner do not use too small a centre drill to start with get some practice with a larger c/drill,if you just need a hole to provide a start for a larger drill use a large centre drill,about 8 to 10 mm body diameter,always lubricate the drill point,the flutes of a centre drill are straight so there is no cutting rake, ok for brass and cast iron but not so good with steel,which means the drill has to pushed a bit harder and is prone to break.On a S7 the tailstock has adjustment to achieve a good fit between the bed ways,carry out this adjustment FIRST to get a nice sliding fit,if the tailstock has had a lot of use it will probably be tighter at the right hand end.then adjust the tailstock to be inline with the lathe spindle,On a badly worn lathe the tailstock can be low which can cause drill breakage and is very difficult to correct.

Kit,

Further to the excellent advice already given: You might like to try "catching the centre" with a hand-held graver.

Have a look at the video on this page, to see how it's done.

Note: There is no need to use a Carbide graver, it's just a good video.

MichaelG.

Kit,

First ensure that your tail stock is correctly aligned with the headstock.

Then try using spotting drills instead of centre drills for starting drills. Spotting drills are now standard practice in engineering and as they have no small diameter pilot they are much more robust than traditional centre drills. (However if you need a centre in the end of a piece of stock for turning between centres or for providing tail stock support you will still need to use a traditional centre drill).

I stopped using centre drills for drill starting a few years ago after trying spotting drills.

You should join the Yahoo group for Myford lathes.
https://groups.yahoo.com/neo/groups/myfordlathes/info

There you will find all sorts of useful information and knowledgeable folks who will be able to assist you in times of need.

Dave
The Emerald Isle

Has it been properly restored or just given a rub over with wet and dry and a lick of paint?

Properly restored, pictures to prove.