Boxford spindle runout

I'm restoring an old Boxford lathe (1949 if I remember correctly, but I could check if this is important) for my entertainment. It came in poor condition and did not cost much. The spindle is causing me some problems. Apart from that, it's looking lovely!

The nose thread (1.5" 8tpi) had been abused but cleaned up nicely. I had planned to use a chuck or faceplate from my Denford lathe but found the register was too close a fit. Various chucks and a faceplate would not screw on. The register could easily be turned down to size but would not resolve the next problem.

I tried a known good MT3 centre in the Boxford spindle. The fit was "ok" but not as positive as I am used to. I then tried several other MT3 shanks and made the same observation. The spindle shows some internal wear and scoring, but nothing terrible. Turning the spindle over by hand the centre was anything but. Runout was about 10 thou / 0.254 mm which is easy to see even without a DTI. Runout on the register itself was less than 1 thou.

Apart from earlier headstock gear damage (now fixed) nothing indicates a bent spindle from being the problem. I have refitted the spindle in its headstock (minus all unnecessary gearing) and found runout to be less than 1 thou half-way along the spindle in each revolution. It looks true to me.

Should I take new measurements before conclusions can be drawn? To me, it seems the spindle bore is poorly machined and/or not MT3 taper. Is it possible that it is something else? Should I reassemble the headstock and attempt to bore the correct and true taper?

Apart from boring bars for the lathe, I also have MT3 hand reamers but don't see how they could resolve this problem.

I was planning to use this lathe for between centre work and so would like to resolve this problem if possible.

Pretty common for those internal tapers to get messed up over the years. First thing to do is make sure your headstock bearings are in good condition and set correctly. Then check if the there are any burrs and dings in the tapered bore that the high spots can be removed with the hand reamer.

If still a problem, then bore the taper to get it running true.Then finish it off the last thou or so with the reamer for a good finish.

If turning between centres the usual way to ensure precision is to use a soft centre in the headstock spindle and machine the 60 degree angle on it in situ every time it is used, to guarantee the centre is running perfectly true.

I suspect that the slightly scored taper may have already been [badly] restored by a previous user.

One approach might be to bore-out the taper and insert a parallel-to-taper sleeve

... Do check the available wall thickness first though !

... You could drop to MT2 if it looks risky.

MichaelG.

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https://www.zoro.co.uk/shop/spindle-nose-and-workholding/sleeves-sockets-and-drifts/turret-socket-3mt-x-1-1-2inch-o-s-diameter/p/ZT1124219X

https://www.zoro.co.uk/shop/spindle-nose-and-workholding/sleeves-sockets-and-drifts/turret-socket-2mt-x-1inch-o-s-diameter/p/ZT1124241X

Edited By Michael Gilligan on 22/03/2021 22:31:48

As said by Hopper :- " If turning between centres the usual way to ensure precision is to use a soft centre in the headstock spindle and machine the 60 degree angle on it in situ every time it is used, to guarantee the centre is running perfectly true."

This is really the only way to ensure any lathe runs true between centres.

Being 1949 vintage your spindle may be 1.5 x 8tpi 60 degree as some very early Boxfords were imported SouthBends and rebadged. I have only ever seen one with a 60 Degree thread. Worth checking before you mess up the spindle or a backplate.

regards

If you have a good MT3 male taper and some blue, you could see if there are any high spots on the spindle taper. They could be scraped down and maybe things might run better.

The Atlas lathe at the museum that is being restored and sold has a MT3 socket on the spindle that seemed ok to look at, but Mike used blue and found a bad spot and improved the running. Unfortunately, we only had one ER25 MT3 collet holder to test it with and it would have been better to have more for comparison.

Thank you Hopper, you make some good points.

The Timken headstock bearings are in excellent condition. I'm quite sure they are not the cause of the runout.

Like you, I initially suspected a burr or ding that could be removed with the hand reamer. I tried (with a very light touch) without improvement.

I suspect you are right about it needing to be bored. I'm reassembling the lathe and once I get a new countershaft spindle made I should be good to go.

I understand why using a soft centre is the best approach and may indeed adopt it in the future, but for now I will endeavor to improve the spindle bore as best I can.

That's not something I had considered, so thank you for the suggestion.

Thank you for raising this - I was aware of this issue but it's always worth checking!

I became aware of the 55 / 60 degree issue after reading the Boxford article on the lathes.co.uk website. However, I'm reasonably confident my spindle thread is 55 degrees. At least, it matches my thread guage spot on and I happen to have a 1.5 x 8tpi 55 degree split die that matches too. All my chucks wind on just fine until they meet the register.

I wonder how I would scrape an internal taper. I'm unsure whether this would be more or less risky than (re-) boring the spindle taper.

I have a good taper and layout blue. In fact, I have enough of the latter to see me out.

Just picked up on your comment, you don't want 'layout blue' you need engineers/marking blue

DaveD

Just DON'T get it on your fingers. Difficult to remove is an under statement!

Howard

If the taper is not responding to your efforts, then get a MT3 soft blank arbor that has a drawbar thread. You can use a length of studding for the drawbar. Drill a blind hole in the end of the arbor, say 1/2", 12mm to take a short piece of steel to turn your centre on in situ. A threaded crosshole in the end of the arbor would secure the tip using a grubscrew. The tip can be re machined to 60 degrees each time the arbor is removed and replaced, and can also be replaced when it is too short. Your centre will be perfectly true despite the socket in the spindle being poor. The arbor will be removed when a chuck is in use. You will need a threaded catchplate on the spindle when turning between centres.

I like that idea. Thank you.

I thought they were one and the same thing, but I'm probably using the wrong terminology. This is what I have https://www.rocol.com/products/blue-metal-marking-layout-ink

No, that's great for marking metal for layout/scribing/cutting lines/ centre-punch dots etc.

I have had the tube of this for 50yrs and not used up yet. marking blue, generally available from various suppliers.
The slightest coating of this on one part and move the two parts together and see where the blue has been removed from one part, this is the 'high spot' that needs attention.
DaveD

edited to add - confirmation to keep off fingers - use a cotton-bud or similar

Edited By Meunier on 24/03/2021 19:44:14

Another quick check is to draw lines along the male taper with a felt pen and let it dry. Then stick it in the socket and rotate it back and forth a quarter of a turn or so a couple times. The lines will be rubbed off at the points of contact and left intact at the loose areas. Gives you an idea of what zone the highpoints are in and where to look for burrs or dents etc.

Glad to see a bent spindle has been eliminated, because it's one of the bad things that can happen to surplus end-of-commercial-life machines. When an accountant or Receiver decides an old machine must go, it's often done carelessly and in a hurry. It's because the space they occupy is often more valuable than the machine, which - even in good working order - is likely to be considered scrap and moved unsympathetically. This includes being lifted by a strap round the chuck, or toppled over and bulldozed out the door with a carelessly aimed fork-lift.

From our point of view it's a crying shame, but accountants are only interested in cash value and selling old machines or even entire businesses can be more trouble than they're worth, especially when time is a factor. The entire Homebase DIY chain was sold for £1...

Dave

Layout blue is often called "spirit blue" This is thin and VERY runny Keep a small paint brush, soley form use mwith it, because it sets hard in the brush, but softens when dipped in again. I use a small pastry brush for mine..

The marking blue is often sold in UK in small tins, under the trade name of "Micrometer blue" This is more like toothpaste in consistency. This is trhe stuff used if you are blueing and scraping surfaces together.

So is the product to check one MT taper against the matching one, internal or external.

Howard