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spindle bearings re chatter cutting steelcantstop

DROMOND LATHE

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Lathe Bearings

Lathe Bearings

In The Model Engineer, issue 2427 of November 27 1947, E.H. Doughty, then Chief Technical Engineer of British Timken Ltd. wrote a lengthy technical letter to refute and address some of the adverse comment that had been made about roller bearings.

stewart wood21/09/2014 10:29:16
33 forum posts

Hi i have a Drumond M TYPE and i have removed and checked the head stock bearings and spindle ,when i reassemble them and try to machine say EN 1A i cant get a good finish . i have tried and checked all the usual things , tool geometry ,slide play , speeds etc, I have a Rohm chuck dia 6 inch and a 3 inch sharp both tried to same effect, i can machine Brass and Aluminium no problem . I think perhaps i am missing some thing when setting up the head bearings . All advice and thought s would be appreciated thanks . Stewart

JohnF22/09/2014 10:01:41
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824 forum posts
92 photos

Stewart, Many years ago I used to rebuild and sell on old lathes, 1960's, now I am not just sure how the head bearings on these machines are adjusted ora if they are tapered or a straight journal? However one thing I learned was that with straight journals you can have the too tight! I.e. No room for the oil and this causes chatter, I found that by allowing a little clearance for the oil, we are talking a minimal amount here the machine would cut just fine, tighten up and it nearly jumped of the bench with chatter.

Try it and see how you get on, hope this helps. John

Ady122/09/2014 10:14:42
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3463 forum posts
513 photos

Theres a bit on headstocks here

Eugene22/09/2014 16:42:45
130 forum posts
12 photos

Hi Stewart,

I've just gone through exactly the same experience with my own M type; no matter what I did the chatter would occur on anything but the finest of fine cuts.

Adjusting the bearings wasn't as simple as the manual suggests. I found that when I pulled up the big bronze nuts to the point where the spindle wouldn't revolve and tightened down the adjusting screw / oiler I'd got just one shot at it, the process isn't reversible so I couldn't fiddle about looking for perfection. It's because when you ease the screw back, the little lozenge piece it bears on doesn't recoil, it just stays put. So lesson one is to get it right first time and then leave it alone.

Even when I'd done that the chatter was still all too apparent. I eventually worked out by (tedious) elimination that it was caused by a sort of concealed end float. The spindle in mine was scored; not badly but enough to be concerned about.  On the shaft near the oiler holes I suspect cast iron or something had found a way in down the oiler hole and done the damage. When I adjusted the end float with the ground collar that bears on the exterior of the headstock spindle nut, I found two conditions; chatter or overheating. Loosely finger tightened gave chatter, a bit tighter gave rapid heating and squeally noises.

My conjecture was that the scoring was enough to resist movement from a finger tight collar, but not enough to stay put under the pressure of the cutting tool. There isn't any much lubrication between the collar and the bronze bearing so when they are brought together under pressure there's a lot of friction. My solution was to place a small needle roller thrust bearing between the two, (ie the bronze bearing nut and the ground collar).

Result ...... chatter gone never to return. If you think this dodge might help let me know, and I can steer you to the bearing supplier. The one I got is an imperial size and a dead fit, no fiddling about required at all, and cost buttons from a UK source.

After I fitted it the note / noise from the spindle rotation was quite different from what it was before which was a bit off putting but it works well enough; I'm turning silver steel at 1050 rpm with a positive rake carbide insert nae bother.

Eug

 

 

 

Edited By Eugene Molloy on 22/09/2014 16:47:25

Edited By Eugene Molloy on 22/09/2014 16:49:02

Edited By Eugene Molloy on 22/09/2014 16:51:57

stewart wood22/09/2014 18:10:45
33 forum posts

Thanks to you all for your advice, the bearings on my machine are the later type, tapered bush into tapered casting with the small tapered block under the lube screw and the C spanner nut on each end of the casting. Eug you are probably right with your idea of one shot at getting it free of play ,sometimes when I set it up its been better than others.I will get back to you on the thrust bearing if I am still struggling .Ady thanks for the link. Another thought ,,could the 6 inch chuck be to heavy ? its got to be 5/6 kgs or more. Stewart

Ady122/09/2014 20:57:47
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3463 forum posts
513 photos

No. Drummond M's are one of the best hobby units you can get, good enough to run all day on mini production runs

The headstock bearings are definitely a pain to set, but it's well worth the effort

This is 36mm rebar I did on my M series, loads of intermittent cuts and a nice finish

 

Edited By Ady1 on 22/09/2014 21:07:31

Eugene22/09/2014 22:56:37
130 forum posts
12 photos

Stewart,

The supplier is "Simply Bearings", the part number is NTA1220 + TRA1220 @ £6.41 ex VAT, and it only takes thirty seconds to fit. I have another M type, a long bed ,wanting some TLC and I'm going to do the mod willy nilly.

NTA1220

If you are going to go through the fag of getting the spindle (and the cursed backgear) out, slip the thrust bearing in immediately you get the spindle back in and before you do any adjusting. End float needs to be done after the bronze bearings have been taken care of.

Best of luck,

Eug

Eugene22/09/2014 23:10:52
130 forum posts
12 photos

Ady1

Thats very impressive, can I ask a beginners question; what is "blue carbide" and what speed and feed do you use?

My carbide inserts would be in a zillion shards trying that. I'll be turning some interrupted cuts on cast iron before long; would you recommend blue carbide?

Eug

Eugene22/09/2014 23:10:54
130 forum posts
12 photos

duplication

Edited By Eugene Molloy on 22/09/2014 23:12:34

Ady123/09/2014 00:57:32
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3463 forum posts
513 photos

what is "blue carbide" and what speed and feed do you use?

They seem to be standard carbide tools, but they definitely aren't as brittle as the red painted carbide tools which chip if you look at them harshly

I just experiment, break some, and figure it out as I go along.

I'm using one very successfully in my newly acquired shaper at the moment, carbide tools are fabulous because they go for so long between sharpening

Speed isn't fast, about 3-400 rpm and I listen to the cut as far as feed is concerned, no violence, it should be a soft hissing type noise. The relief angles are very shallow to maximise tool tip support and done by eye

The key to successful carbide work on a hobby lathe for me seems to be stiffness, everything I do is geared towards maximising stiffness and I have made a pretty massive toolpost to help

edit: which reminds me. You don't need to use the top slide unless you are doing tapers

I use a muckle toolpost on the cross slide

Edited By Ady1 on 23/09/2014 01:00:19

Ady123/09/2014 01:15:15
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3463 forum posts
513 photos

I'll be turning some interrupted cuts on cast iron before long; would you recommend blue carbide

I would do cast iron on the backgear and use an upside down blue carbide tool on the rear of the cross slide

The parting tool is my favourite, with a tidy up on the green grit wheel to give it reasonable sharpness

You can see in photo 2 the swarf is in front of the toolpost because I do a lot of work with an upside down tool (which saves me worrying about the tool setup height)

If you cut from the rear side on the backgear the amazing mess cast iron makes is largely eliminated and you have a neat pile of iron filings down the back of the lathe which can be sucked up with a vacuum

stewart wood23/09/2014 07:51:32
33 forum posts

Thanks again for your help , my enthusiasm as been re ignited . I was given this lathe a couple of years ago and spent a few quid on a motor and lead screw nut [I had made ],a complete strip down paint and rebuild only to find I couldn't stop the chatter .I will have another go re armed with new info . Stewart

Ady123/09/2014 09:40:36
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3463 forum posts
513 photos

You need to sort that chatter out first before using any carbide. Use HSS until you can do a constant cut which gets blunted by the amount of work the lathe can do. That's what made me go for the switch to carbide, I realised I was spending a lot of time tidying up HSS tools and wondered if I could use a longer lasting material.

GL

Edit: The key for me has been practice

Practice practice practice practice

I have turned a load of material from the scrapyard into buckets of swarf to get a bit of experience

That lathe you have is one of the best hobby lathes ever made, which is why the Ministry of Defence churned them out during WW2

BTW You will find the leadscrew clutch hugely useful once you get going because it allows you to semi automate your work

Edited By Ady1 on 23/09/2014 10:05:43

Eugene23/09/2014 11:04:35
130 forum posts
12 photos

Stewart,

When I was playing chase the lady with the chatter the decision was to start at the cutting tool and work back down the drive train from there looking for problems; dead logical. Tool holder, tool post, topslide gibs, crosslide gibs, carriage lock, carriage fit, bedways, bearings, spindle, Uncle Tom Cobbleigh and all. The final thing to check, and thus the very last link in the chain was the end float adjustment, and guess what? That's what being logical does for you.sad

As Ady1 recommends I even ditched the topslide altogether and finagled a tool post to sit directly to the cross slide; it didn't help me with the problem in hand but it's not a bad move if you aren't turning tapers and such.

Eug

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