Proxxon lathe PD 400

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Martin,

Hopper's right, of course; but may I add one more to the list of questions without causing offence ?

Have you had [say] a parting tool 'dig-in' recently ?

It strikes me that the most likely thing to move the spindle by so much would be a sudden loading.

... Fingers crossed that we're missing something more-easily rectified !!

MichaelG.

As mgnbuk asked does tje taper appear when you turn the outside diameter ? If it does is the taper the same as the internal one ? Is the cutting tool sharp and how much overhang do you have ? I have seen a scenario where the boring bar was sticking out a long way from the toolpost and all that extra leverage caused the tool post to walk around . Are you boring using the saddle movement or a compound slide ? What sort of stick out do you have from the chuck , ie how far does the workpiece stick out from the chuck ? What about the chuck jaws are they in good cond or maybe bellmouthed ? What is the machine mounted on ? Steel ? wood ? or something else? wood can warp over time and put a twist in a lightly built machine , you can check this with a spirit level easily enough .

Can you post some photos of your set up ?

0.003 per inch doesn't just appear out of nowhere unless something got bent !

I would re test using nice sharp tooling set up on centre height with very light cuts and do both inside diameter and outside then measure it all , this will minimase tool deflection, machine flex , workpiece flex and tool push off .

Bearing pre load , i just used a peg spanner on the nut and a shifter (adjustable wrench) on one of the chuck jaws and nipped them up - don't need to hang off it like a gorilla though ! I have never had a problem doing it this way on my three lathes that have taper bearings . If the rear bearing inner is tight on the spindle you may have to crank on it a little harder just to make sure it is seated then back it of and nip it up , i'm giving it about 1/16 of a turn on the nut after it contacts the bearing with firm hand pressure ( tighten as much as you can by hand then use the spanner) .

If the bearings show no signs of damage like pitting chipping ,scoring or discolouration they are fine for re use , usually the first signs of bearing play or wear is chattering , if it is not chattering and machining nice and round the bearings are ok .

One last thing check all of the gibs are adjusted correctly so nothing is moving around on you , wouldn't be the first time i have seen a cross slide work itself along because of vibration or a saddle cock itself sideways when machining ! I used to have to operate a severely flogged out lathe ( we are talking bed wear closer to a millimeter than anything else ) and trying to turn anything near parralel was impossible even though the wear was consistent along the bed as the saddle could wander around a lot especially when power feeding .

Edited By XD 351 on 17/05/2018 07:58:57

Again, I thank you all for your suggestions ... it seems there are lots of people way ahead of me as regards long-term lathe maintenance

MICHAEL ... the note on page 20 about the bearings ... I think my total running time is way over 6,000 hours ... over 14 years even at only 1 hour per day it would be about 5,000 hours ... some days the lathe has actually been run for 10 hours ... so the actual total could be 15,000 hours or more ?? ... even if the roller bearings still look smooth they could easily be worn away ... A long time back I swopped the Proxxon motor for a 3 phase unit from Newton Tesla ... this is wonderful but I suppose it meant the lathe was running for longer periods with no pauses for belt changing or any other needs for stopping.

HOPPER ... the lathe is in constant use for all sorts of short items, but I have not needed to make any cylinders with a matching piston for 2 or 3 years ... I assume the wear has happened in that period ... cutting any test bar, the end nearest the tailstock is the largest diameter ... I would reckon the spindle is now pointing at the wall behind the lathe when it is cutting.

ADY ... I do not understand what Proxxon would mean by "adjusted by a specialist" ... I have tried the rollers with lots of pre-load and also very little pre-load ... changing the one at the rear with a new one is easy ... I shall buy one and try it.

If the headstock casting is distorted I wonder if I have helped to cause this with too much pressure over the years by using the parting-off tool supplied by Proxxon ... it is 3mm wide and needs quite a shove to make it cut ... a lot of the work could have easily been done by using something half that width.

If I get to feeling masochistic I may ring Proxxon for either advice or the cost of a new headstock assembly and also the bed.

Does anyone want to guess at the price ??

martin

Possibly half the price of a new machine.

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[ With my 'wishful thinking' head on ] ... If you caught the right Proxxon representative, on a good day, they might thank you for the 'testing' you have done on their behalf.

If the bearing housing in the headstock has been mis-aligned by 'normal use' then they should be interested in doing a 'failure mode analysis' ... A company with their reputation might be surprisingly grateful.

... We live in hope !!

MichaelG.

I think I'd be tryng new bearings before I sprung for a new headstock. If you are still having trouble getting the old race out, heat the surrounding casting with a propane torch or heat gun. I would not put oxy acetylene near aluminium machine tool components. Too easy to warp things. You might have to make some kind of puller using a lenght of threaded rod and suitable washers and spacers etc to pull the race out.

Ditto getting those allen bolts out of the headstock to remove it from the bed if you decide to go that way.

To all the kind-hearted gentlemen above ... yet again I say thank you ... reading how you each would tackle the problem has very much sorted it out for me ... I did not know whether to aim at the bed, the bearings or the headstock casting itself ... getting a new rear bearing was by far the cheapest and easiest option ... taking a concensus of what you all said I have now fitted a new rear roller bearing ... magic !! ... the amount of taper was 3 thou per inch ... it is now less than half a thou ( 0. 0004 ) ... when I can wangle the front bearing off the spindle I am very optimistic the lathe will be properly parallet again ... as MICHAEL has put above, we live in hope.

I am extremely grateful for all the different bits of advice from people who know much more about lathe maintenance than I do.

martin

Great to see you get a result

You are now an "expert" !

What kind of preloading did you use? Handy for anyone looking in, I bet you won't be the last to do this procedure.

Best possible outcome, Martin

... upon which basis, it's been a joy to share the journey.

MichaelG.

Yes please! I too have one of these machines, and (although I'm well under the 6000 hours) I was intimidated by the 'expert' thing in the manual. But time may come...

Robin.

Edited By Robin Graham on 18/05/2018 23:48:10

TO ADY 1 and ROBIN please ... for the preload I ended up with a very light preload ... I did try lots of pressure as well but the cut was just as good lightly loaded ... I clamped the circular nut as hard as possible by hand, then used a small hammer and a flat ended punch to move it about 1/16 of a turn ... this was suggested by one the replies above, I believe ... if I had to guess at the reading on a torque wrench it would be 20 or 30 foot pounds ... not much ... the bearing came from Arc Euro Trade, cost £16. 99 and has a code number 30207 ... when I get the other bearing off I will be able to see if it has the same code number ... that I.D. mark is facing the chuck backplate, but it does look the same.

I look forward to seeing how long this bearing lasts ... I shall try to remember to keep checking diameters on a test bar over the years ... just to make sure about the taper.

Thank you all, martin

On Proxxons spare parts list for the PD400 they list the 2 headstock bearings with the same part number, they are probably both 30207 bearings. How do you find the PD400 in general having used your one for several years. I have thought about possibly getting a PD400 for some time now but was a bit wary of the being so light in weight. I don't do particular heavy work more just fairly lighter turning. Glad you getting your problems resolved with the unwanted taper.

Martin H

Edited By Martin Hamilton 1 on 20/05/2018 14:16:22

Glad you got a result (and new-found expert status!). I might have misread before. If your problem is getting the bearing off the spindle, with the assembly already removed from the ally headstock, then heating the bearing race with oxy-acet should get it off. Just don't overdo it with red heat or anything like that. About 200 to 400 degrees C should do it. (Spit-sizzlin' hot).

TO MARTIN H ... so far no real problems ... this bearing wear is the first major problem ... the lathe has been used and used and ... etc. for a long time ... I did swop the motor for a 3 phase variable speed drive ... that was the best thing I have ever done ... the original motor was advertised as continous run ... mine was not ... after 30 or 40 minutes it got hot and noisy !! ... very long story ... but I eventually bought the CL 400 unit from Newton Tesla ... the new motor fits neatly behind the lathe at the left side.

The carriage adjustment screws are underneath ... 2 pieces of heavy timber 6 x 3 inches are useful to prop the lathe up ... the tailstock clamp was a short Allen key ... I have swopped this for a long Allen key with a tee handle.

The lever to clamp the carriage to the leadscrew was very tempting to move when screw cutting ... I drilled a hole in the front of the casting to put a lock on it.

There was a misprint in the chart for screwcutting ... given the change-wheels supplied it was not possible to cut a 16 TPI thread ... no doubt this misprint has been corrected by now.

I would buy a parting-off tool about 2mm wide .... the one supplied is 3 mm ... for small bits of brass it is very heavy to use and wastes lots of material ... a smaller tool might also save some of the sideways wear.

This lathe has spent its life cutting brass, bronze and gunmetal ... it has also been used for small pieces of mild steel and stainless steel ... if it was cutting lots of steel 2 inch diameter I think it would have died a lot quicker.

Would I buy another ? ... definitely ... for the smaller sizes of material I use it is perfect ... if I just ate beans on toast for the next year I would buy one now and leave it set as milling machine.

I did buy the faceplate and 3 chucks ... 4 jaw self-centering is superb.

TO HOPPER ... I like the phrase "spit-sizzlin hot" ... your workshop sounds just the same as mine ... I am not an expert in anything ... my wife says I know nothing !!