Lathe Drilling

Hi all, I'm having real problems drilling on my lathe recently and I can't seem to figure out why. My lathe is a Chester DB8VS and I'm noticing that when I start to drill, the drill bit is wandering so I'm therefore ending up with a larger hole than I require. I doesn't matter whether I centre drill to the chamfer, just the tip, make the smallest mark or even spot drill, the drill still wanders. I've tried pilot drilling, step drilling, drilling straight to size. I've spent hours messing with my tailstock alignment and even bought a test bar so that I can align it better in case it's that. Granted it's not perfect as even the amount of slack in the quill lock causes some play but I was confident that I managed to align it within 0.01mm over the length of the test bar with the quill fully extended. However, each time I disassemble my alignment setup and re-setup I would see some movement (the test bar fits in the taper on the headstock and ran to a dead centre in the tailstock). I also checked the height alignment which I can't quite remember but was happy with, I think it was around 0.020/0.025mm. Originally it was that bad that it was drilling an 11/32 (8.73mm) at 9.5mm over a 10mm depth so you can imagine my frustration. Trying to run my 9mm reamer down it and it obviously wasn't touching it. With the new alignment I've managed to get it working better and thought I'd cracked it, however last night I noticed wander on a 4mm drill (standard length). I even thought it could be my drills as I do only use a cheap drill set (albeit a new one) but have also borrowed expensive drills from work with the same results. It makes no sense to me at all, if I'm centre drilling/spot drilling from the same chuck in the same tailstock how is the drill able to wander so much that it's easily visible? I've tried with coolant, without coolant, feeding faster, pecking etc. At one point a slower speed (than recommended for drill size) made it a lot better but that didn't work at all last night. I'm starting to think that it's a combination of little issues and movements with it being a Chinese lathe. My dad does have the same lathe though and his drills perfect. We've both been scratching our heads on this one as when he uses mine with his drills and chuck even, he gets the same wander. Am I missing something, has anyone had any similar issues with a similar sized lathe and managed to solve it. As it's not glaringly obvious to me it's driving me mad and I'm spending less time in my garage as a result. As a side note there is no play in the headstock bearings. Thanks for taking the time to read this, I've tried to include as much information as I can.

Dave

If you have a couple of DTI's try using them to track down the source of the wandering by elimination while doing some test holes.

One on the drill shank, and one on the side of the chuck if possible - that will tell you if the drill is wandering in the chuck, or they are both wandering together - eliminates the chuck. Move the one on the drill to the quill. Is the chuck wandering relative to the quill, or are they wandering together. Move the one on the chuck to the side of the tailstock. Is it the quill wandering in the tailstock, then tailstock relative to the bed.

You might want to do the tests both horizontally and vertically.

Once you know which two parts are wandering relative to each other you might have a chance of fixing it.

PS - also check it's not the stock moving in the chuck!

Edited By Peter Cook 6 on 26/10/2021 10:49:27

I bought a set of drills from ebay advertised as quality cobalt and they were a joke

Unhardened bits

wobbly tips

Then there's your spindle and bearings

And your chuck

Can you tailstock drill into the chuck ok

Can you chuck drill into a tailstock pad ok?

If there is ONE thing lathes are good at, it's drilling holes

Edited By Ady1 on 26/10/2021 11:31:54

Try checking the centreline of the drill chuck against centreline of the chuck shank.

If you have taper sleeves you could mount the shank in the spindle taper then check the concentricity of a known straight bar held in the drill chuck with spindle rotation. Or grip said bar in drill chuck, other end of bar in a decent 3-jaw, then see how true the chuck's taper shank runs.

I'm suggesting this because, if you've tested multiple drill sizes, I'm wondering if the centreline of the chuck is at some small angle to that of the taper shank. Must admit I can't ever remember having seen that condition.

Try comparing a centre held in the 3 jaw turned from a piece of rod after using the test bar, something is out of line

An good way to check the tail stock alignment is to put the spigot of a lever DTI in the 3 jaw chuck & rotate the probe inside the tail stock taper, obviously this won't tell you if the tail stock travel is parallel to the lathe axis but is a easy test to start with.

Tony

To see if the tail stock barrel is lying on the lathe axis extend the barrel but do not lock it but lock the tail stock body as if drilling, rotate a DTI around the barrel outside diameter at it's front and back, if aligned both positions should clock true.

Tony

Thanks for all the replies guys, a lot of good information for me to work through there. It's one of those problems that's really got me stumped, and I don't have enough turning experience to be able to just follow a methodical approach and bottom the problem beyond the things I've already tried. I've wasted hours and hours on this already and I'm not really getting anywhere as it just doesn't make sense. Even if something wasn't aligned correct, surely after spot drilling then the drill should at bare minimum not wander on entry. I think of it as in drilling a hole in a cylinder, with an accurate centre drill the drill shouldn't wander... I'm an engineer so consider myself to be a logical thinker and I just can't get my head around this one!

I do have a couple of DTI's so will work through checking the alignment and I'll get my hands on a taper drill to use in the tailstock without the need for a chuck. That will be interesting to see the outcome of, as will drilling from the chuck.

My test bar is the type that has a taper 1 end and fits into the headstock as I said. I was hoping it would be centre drilled both ends to allow me to mount it on centres but it isn't unfortunately. I do wonder if a bar between centres would show different results, especially if ran from a centre made and held in the chuck.

Thanks for all your suggestions, I will slowly work through them all and see what I can find.

Having the same lathe I can say I have no problem. Of course as you can set a tapper on the tailstock there is always the possibility not to be exactly on zero (and here I wouldn't go for their marked zero but for something you test)

I understand you have checked the centres (which is easy as the machine comes with 2 dead centres for head and tail stock, and which I rarely use as I prefer a live centre)

I suppose you checked also with the quill full in and full out so there is no taper setting error.

And this is something you know for sure, I just say it so that it is not forgotten. When you are drilling - use a drill slightly smaller than the diameter you want, if the step between the pilot drill and the final diameter is too large the hole will always be too big. So for 8.73mm I would use approx 3mm as a pilot, followed by 8.5, followed by 8.73

And just a word about Chinese machines: I had an EMCO (old one, made in Austria) for more than 30 years - and recently upgraded to the Chester DB8VS. The DB8 is far more precise and accurate then the EMCO ever was!

Regards,

Gerhard (made in Austria like his old EMCO...)

Edited By Gerhard Novak on 26/10/2021 13:57:02

Edited By Gerhard Novak on 26/10/2021 13:58:00

Hello Squarepeg,

Your post opens by saying that you are getting these rogue results recently. Does this mean the problem has developed or is it a case of trying drilling for the first time? I find the latter hard to believe.

You say that you father also gets wander using your drills and drill chuck on his identical lathe when he normally get good results. Have you tried things the other way round and used his gear on your lathe?

For my money this is beginning to look like a fault in your drill chuck, worn jaws, swarf inside or some such fault

Regards Brian

Or the drill bit/s not being sharpened correctly ?

No Brian,

My dad does have the same lathe though and his drills perfect. We've both been scratching our heads on this one as when he uses mine with his drills and chuck even, he gets the same wander.

Dave,

Either swap your tail stock for your Dads if it's the same one or inspect it's taper for burrs.

If the drill lips are not the same length, it will wander and cut oversize because the intersection of the lips is not on the axis of the drill.

It might be worth ensuring that the tailstock is DEAD inline with the Headstock, and then try with another drill to see if it just the one frill that wanders or whether others do (Preferably drills that have not been ground at home.)

This assumes that there is no excess clearance or dirt between Tailstock and bed ways in both planes.

Howard

Hi Gerhard,

At first I was checking the alignment by fitting both centres and gripping a blade between them and getting it as level as I could. Quick and dirty I know but rather effective and suitable for what I required.

Using the test bar, I only checked with the quill fully out in the belief that this would amplify any error. I assumed that any taper would show over the length of the test bar (~300mm).

With the hole last night being 4mm, I didn't bother to pilot and it was wandering by a fair amount. I just can't get my head around where it's wandering too if there's a centre there on the same axis. In regards to step drilling there's lots of conflicting information even in these forums, some people say up to around 10mm don't even pilot and others use multiple steps. I've tried many different ways in the hope to find something that stops my problem.

I do agree about Chinese lathes to be fair, with todays technology the repeatability and accuracy available is very good. I just know they also lack quality control at times and therefore have a bad reputation. Other than this issue I am pretty impressed with the lathe.

Brian, to be fair I only bought the lathe this year so haven't had loads of use and I only more recently started doing more accurate stuff so it's hard to tell of anything has changed on that regard. As Dave pointed out I've already tried what you suggested, so I know it's a lathe issue and not a tool.

J, I did think that but have now tried many different drills with the same results but thanks

Dave, good shout. Funnily enough that's what I said to him at weekend and is definitely on my list to try. I can't see any burrs anywhere and I've given it a good clean so I'm happy it's not that. I guess I was just hoping I was being daft and missing something simple or someone else would have had the same issue and solved it. I don't think I can face aligning another tailstock yet even though I think I've become reasonably good at it with all the recent practice .

Thanks for all the suggestions, really appreciate the assistance!

The process of accurate drilling came up some time back but was not talking about tailstock drilling, it was about basic drilling or milling machine drilling. Using a centre drill is the wrong thing to do as the angles are all wrong and the outer edges of the drill will contact the workpiece first and cause wandering. The use of a spotting drill with an angle greater than the standard drill point should be used, so for a 118° drill the spotting drill used should be 120° or more. This will guide the drill into the centre before the edges contact the workpiece and cause wandering. You can test the effectiveness of this by using a turning tool to produce a 120° recess and using a standard 119° drill in it.

Another thing you can do is use a stub drill to start the hole at the desired diameter then follow up with a jobber drill. Standard jobber drills are like a twisted ribbon and can flex a lot.

Martin C

This thread covered this subject

Edited By Martin Connelly on 26/10/2021 19:01:19

Dave,

As you have never mentioned normal turning operations and you set the centres with the ruler test, did you try rotating the spindle?

It could be the work wobbling the drill, which would mean your chuck is off.

A 4mm drill will wobble if you have a centre pip left by facing.

Edited By Dave Halford on 26/10/2021 20:00:29

OP mentions centre and spot drilling

Tony

I often see videos of drilling in the lathe. It is common to see the centerdrill move laterally as the point begins to penetrate the work. That tells me the tailstock is not aligned with the spindle. Many times this is due to the front of the tailstock base being worn, or the quill is loose in the tailstock body. If the base is worn shims can be placed between the tailstock base and the body.

In problems like this always look at the absolute basics first......

If DB8 is like it's Warco equivalent then it comes with a centre for the spindle throat and another for the tailstock,.......find these and fit into the respective throats........slide the tailstock up so that both centres are 'point to point'....check exact accuracy using a glass.

..........Make sure that the throats are both clean by shining a light up and having agood look!.......Also make sure no swarf or foreign body is under the tailstock.

If both centres align perfectly, replace tailstock centre with drill chuck holding a centre drill only (nothing else) and repeat alignment test......