Author Topic: Finishing problems  (Read 23671 times)

Offline Darren

  • Madmodder Committee
  • Hero Member
  • *****
  • Posts: 3795
  • N/Wales
Finishing problems
« on: November 11, 2008, 04:00:50 AM »
Not sure where I should put this?

I have a problem with my 7x12 when using the carriage feed. Mainly when finishing a length of work it leaves a mirrored patten of the lead screw pitch on the surface.

This means I have to take the last cut with hand feed. This as you can imagine really spoils this little lathe and it would be great if it could be sorted.

But how? Suggestions most welcome...

Regards
Darren
You will find it a distinct help… if you know and look as if you know what you are doing. (IRS training manual)

Offline Bernd

  • Madmodder Committee
  • Hero Member
  • *****
  • Posts: 3688
  • Country: us
  • 1915 C Cab
    • Kingstone Model Works
Re: Finishing problems
« Reply #1 on: November 11, 2008, 09:25:34 AM »
Darren,

How about a pic of the finish. Does it squeel, chatter, what?  That might help. Also make sure your speeds and feeds are correct. Sometimes to light a cut cand cause that. Make sure things are tight.

Bernd
Route of the Black Diamonds

Offline Darren

  • Madmodder Committee
  • Hero Member
  • *****
  • Posts: 3795
  • N/Wales
Re: Finishing problems
« Reply #2 on: November 11, 2008, 01:34:38 PM »
Hi Bernd,

No nothing like that, it cuts really smoothly, just leaves a faint impression of the lead screw thread mirrored on the work.

I decided to have a better look today to see if I could improve things.
First I put a dial gauge on the bed and measured the carriageway as it was powered up and down the lathe.

To my horror I saw the carriage lifting up and down by 2 thou over it's whole length :bugeye: 

So off came the leadscrew and stuck it in the bigger lathe for further measuring



Between the leadscrew section and the bearing surface I measured 22 thou off center !! You could see it clearly going up and down as the lathe was turned by hand.
The tail end was fine, or at least better at 2 thou.

So what to do, buy another? Would that be just as bad............but then I thought what could I do with this one I already had? I mean, not much to loose was there.

So I attacked it and did this, pic's should explain, I had some sintered bearings from another project.


Truing the bearing area of the shaft and reducing it to fit some bearing I had.




Here I'm reducing the outside diameter of the bearing to fit into the mini lathes pillow block.



Installing the bearings, I had to use two, one at each end. I used a press as I wanted them tight fitting.



Fully home



Back on the lathe,
Looks good to me....





But did it work...?

Well the carriageway now only moves 1/4 of a thou, not perfect, but a lot better than it was. Certainly can't do any harm can it. Maybe I'll have another look at the tail end.

Will put it to the test shortly and see if the end result improves....

Regards
Darren

« Last Edit: November 11, 2008, 01:38:22 PM by Darren »
You will find it a distinct help… if you know and look as if you know what you are doing. (IRS training manual)

Offline Darren

  • Madmodder Committee
  • Hero Member
  • *****
  • Posts: 3795
  • N/Wales
Re: Finishing problems
« Reply #3 on: November 11, 2008, 03:10:47 PM »
Tried a test to see if it was any better, it's improved a little but not good enough.

Here is an older piece that is worse than it looks, and it looks bad !! You can very easily feel this pattern.




In the chuck is a piece i've just tried after modifying the leadscrew, as you can see it's not much better. A little, but like I said, it's not good enough.



Regards
Darren
You will find it a distinct help… if you know and look as if you know what you are doing. (IRS training manual)

Online Brass_Machine

  • Administrator
  • Hero Member
  • *****
  • Posts: 5504
  • Country: us
Re: Finishing problems
« Reply #4 on: November 11, 2008, 03:50:22 PM »
Darren,

I had a similar problem on my 7x lathe. Not quite as pronounced though. I fixed it by a combination of feed speed and using a HSS insert.

I know that isn't much help.

Eric
Science is fun.

We're all mad here. I'm mad. You're mad.

Offline Darren

  • Madmodder Committee
  • Hero Member
  • *****
  • Posts: 3795
  • N/Wales
Re: Finishing problems
« Reply #5 on: November 11, 2008, 04:34:34 PM »
Ah, I wonder if others out there have similar probs with these small lathes?

Does anyone else on here use a 7x12 or similar?

I'm wondering if it's just down to the lightness of these machines, or at least the carriage.

Darren

I've threatened the missus that there may be a new addition after xmas, I'm toying with several possibilities.
A larger Smart and Brown, a Cardiff or a Colchester Student.  Be nice if I could see something larger in action to make further assessments.
Alas I don't know anyone locally with a lathe, let alone a bigger one. Or a workshop for that matter.

N Wales,

Here's some stuff I did a few years ago, http://homepage.ntlworld.com/darren.dean/index.htm
You will find it a distinct help… if you know and look as if you know what you are doing. (IRS training manual)

bogstandard

  • Guest
Re: Finishing problems
« Reply #6 on: November 11, 2008, 04:45:02 PM »
Darren,

I am not an expert on this sort of problem on a lathe, but have come across a similar situation on another type of machine.

Has it been like this ever since the machine was new, or is it a fault that has appeared over time?

It looks like the far side of the saddle is 'dragging', that is where the leadscrew is driving the one side, and the other side is lagging behind, then when the lag gets too much, it springs forwards to catch up, and then does the same thing over again. It only takes a few very difficult to see thous to cause a problem. It might not happen when using the handwheel because of the different moment forces involved.

I would try holding the leadscrew side rigid (or just engage the half nuts) and try to move the far side of the saddle backwards and forwards. If there is play there, you should be able to adjust up on the jibs to reduce the fwds/back play. But before doing all that, make sure you are not running dry on the far side, the lube should be on the top edge and the far side plus the far bottom of the slides.

If that isn't the problem, try to only partially engage the half nuts, so that it is only just driving the saddle, and see if the fault is still there. If it disappears, that would point to your problem leadscrew, and you might get around it by adjusting the engagement force on the half nuts. Not an ideal situation, but if it gets rid of it, you are halfway there.

That is all I have, hope it helps with your problem.

John

BTW I am in fairly easy striking distance. Crewe, Cheshire. Plus you have Ralph in N. Wales.

Offline Darren

  • Madmodder Committee
  • Hero Member
  • *****
  • Posts: 3795
  • N/Wales
Re: Finishing problems
« Reply #7 on: November 11, 2008, 06:04:51 PM »
Hi John,
Had another good look taking on board your comments. I've had this lathe about two years and it's always done it.

I've always thought there was a lot of movement in the carriage, up/down and rocking horizontally side to side. But then I've little to compare it to.
My S&B is a plain lathe and thus locks its carriage down hard to the bed. Movement is manual only.

On the 7x12 there are adjusters underneath, ie when tightened they pull the carriage down, no gibs as such, just some crude plain bars.
The thing is, the bed seems narrower at the tail than the headstock. If I adjust the "gibs" for mid point along the bed it becomes very slack at the tail and impossible to get near the headstock.

It could be dirt, I doubt it but I'll gunk it all down and give it a good clean and try again.

Will post here when that's done.

Yep, Crew is not too far, Ralph must be in between then.

I'm nr Porthmadog, well almost.....just think model trains that are put to work..... ;D

Regards
Darren
You will find it a distinct help… if you know and look as if you know what you are doing. (IRS training manual)

Offline Divided he ad

  • WARNING: LIKES SHINEY THINGS
  • The Collective
  • Hero Member
  • *****
  • Posts: 1950
  • Country: gb
  • Between Chester, Wrexham, ruthin & Holywell :-)
Re: Finishing problems
« Reply #8 on: November 11, 2008, 07:28:55 PM »
Hi Darren, I've been reading your post and was thinking of play in the saddle too... Maybe undulations in the lead screw moving the whole saddle?

Well it's a thought. The tapered bed is a new one on me though!

I've also checked the distances involved.... A good trek!!

http://maps.google.co.uk/maps?f=d&saddr=mold&daddr=A494+to:52.987511,-3.390656+to:Porthmadog,+Gwynedd,+United+Kingdom&hl=en&geocode=%3BFbVWKQMdQo7M_w%3B%3B&mra=dpe&mrcr=0&mrsp=2&sz=10&via=1,2&sll=53.078353,-3.637848&sspn=0.52055,1.450195&ie=UTF8&z=10

(personally I'd grab and drag the blue line over to the 494 Road.... It will travel much faster than the winding roads, no matter what the computer says!)

Crewe works out at just shy of 2 1/2  hrs.

I've only got a 9x20 and John has the now super acurate beastie.... Not too sure of it's size and can't remember the name!!!  (the memory is getting worse with age!) it is a nice big fella with a gap bed and I'm sure 20+ inches between centres (I'm sure John will clarify?  ;D ) I'm sure visits could be sorted..... You'd have to be ready for a messy cramped workshop where two can barely fit at mine though!! It's only just over 6'6"  square!  :)


It'll be interesting to see your findings.


Ralph.

I know what I know and need to know more!!!

bogstandard

  • Guest
Re: Finishing problems
« Reply #9 on: November 11, 2008, 08:03:30 PM »
Darren,

The bed must have been machined that way, because when a bed wears, it always does it the opposite to what you have. It always tapers towards the head, and when you adjust, you have trouble getting it to the tailstock end.

Maybe after 20 to 30 years of hard use, it will wear itself parallel.

How long is the bed? Because if you really want to fix it well, it might fit onto my mill, and I know I can get it within a thou parallelism, which must be better than you have now.

This is my new 'beastie' as Ralph calls it.

http://www.chesteruk.net/store/crusader_lathe.htm

John

Offline Darren

  • Madmodder Committee
  • Hero Member
  • *****
  • Posts: 3795
  • N/Wales
Re: Finishing problems
« Reply #10 on: November 12, 2008, 10:23:10 AM »
Hi John, Ralph,

I took some measurements of the 7x12 bed

Length
Total 25"
Front of headstock to tailstock end 20"

Width
Head just under chuck 82.74mm
Tail 82.53mm
Difference 0.21mm/8.19 thou


Bed thickness for carriageway
Head back 8.57mm
Tail back 8.23
Difference 0.34mm/13.26 thou

Head Front 13.53mm
Tail Front 13.38mm
Difference 0.15mm/5.85 thou

As  you can see, not too clever are they..

Ralph, small workshops, clutter, loosing things sounds familiar.

I have a mate in Holywell and often take the misus to Flint shopping.

So near enough I'd say.... ;D
« Last Edit: November 12, 2008, 10:25:40 AM by Darren »
You will find it a distinct help… if you know and look as if you know what you are doing. (IRS training manual)

bogstandard

  • Guest
Re: Finishing problems
« Reply #11 on: November 12, 2008, 01:05:00 PM »
Goodness me Darren, that isn't a lathe, it's a banana.

It is no wonder you are having trouble with it. That needs some serious work to get it to be a precision machine, but nothing should be discarded until all hope is lost. Getting the bed casting sorted should be a fairly straightforwards job. The hard bit is getting all the other bits to fit correctly afterwards. You will most probably find that the saddle, head and tailstock castings will be in the same sort of ballpark.

They were most probably assembled by having a large number of each casting, and were swapped about until you got something that almost worked. Then it was stuck in a box, and sold.

If you need assistance, don't be afraid to ask. It is most probably only a good days machining worth to get it something like.

John

Offline Darren

  • Madmodder Committee
  • Hero Member
  • *****
  • Posts: 3795
  • N/Wales
Re: Finishing problems
« Reply #12 on: November 12, 2008, 02:45:53 PM »
Yes John, I didn't think it was too clever!

I sorta gave up with it, perhaps understandably you might think, and bought a Smart and Brown 3ph Model L lathe about a year ago.

This is a capstan lathe that came with a 6 position semi auto turret and a twin tool cut off slide. Great for small production work if you want to make many identical small parts. At the time it was just what I needed and did it's job admirably. 100 small parts in a hour is easily achievable once it's been set up which can sometimes take a while.
Since then I've bought quite a bit of tooling for the capstan so that job is now much easier thankfully.
Anyway, the important bit is that it has paid for itself easily.

Then I bought another S&B L lathe just for a compound slide and tailstock. Ever since then the mini lathe has seen almost no use. The compound slide looks ropey to say the least, but it is nice and tight and cuts superbly accurately.

Alas it's basically just a plain lathe, so no feed and no screw cutting facilities. It can also only make small length parts, max about 3" long up to 9" diameter.

It was only the other day I had my first go at cutting a thread on a lathe. For some reason I'd been putting this off thinking it would be a bit difficult. I was so wrong, the little lathe does this just fine with a nice finish too. I look at it sometimes and think what a nice dinky little thing the 7x is . If only it was a little better built.
I'm not knocking it, I think they are great and also think I was just unlucky with the build accuracy of mine. Others manage well with theirs, for a long time I just thought is was me.

Anyway, back to the issue at hand, yes it would be great to have an accurate mini lathe. If it was I'd never part with it. Ever !
As for needing help, I am not the one to put it right. I simply don't have the skills or tools needed.

One day maybe, but not for a while yet !!!

But, I have one question. I certainly don't expect anyone to spend a day machining out of sheer kindness, and I suspect you may fall into that category John.
So, as I am hankering for another larger lathe, ambitious? maybe...gotta push forward eh..would I be better off putting efforts towards that end or is a super accurate mini lathe worth having as well?
Genuine question as I do not know the answer to that.

Regards
Darren





You will find it a distinct help… if you know and look as if you know what you are doing. (IRS training manual)

bogstandard

  • Guest
Re: Finishing problems
« Reply #13 on: November 12, 2008, 03:39:44 PM »
Darren,

As a lot of model engineers find out when they come to me, I happily help out, with no charges at all, except for the coffee, that comes at £20 a mug. Just joking of course, it is in fact £25.

Any lathe, no matter how big or small is worth putting time into. I have restored a few lathes, and my last one was a prewar Atlas, which I had used up until a few months ago as my only lathe, it kept me going for 15 years, and when I sold it, it was machining better than if it was new.

To me, your little lathe would always be a machining asset, and would really be worth keeping if it was put on the right side of good. I don't mind putting a few hours into it, F.O.C. If you could leave it with me, I could just plod along on it as and when I have some time spare. It takes up no room, so it could go into my back metal prep shop. The offer is there if you want it. I would suggest you have a private word with Ralph to find out my 'rules'.

Choosing a good second hand lathe is like walking into a minefield blindfolded.

In the UK, you can't go far wrong with one of the UD boxford range, preferably the AUD. They were the ones that were installed in schools and other educational departments, and if you can get one of those, they had hardly ever been used. They can be picked up fairly reasonably, and they are almost bombproof. It is a fairly easy motor swap to convert from 3 to single phase, but it is always worth considering putting a converter on them to run 3 phase from single. Imperial machines are the easier of the machines to get cheap spares for.

http://www.lathes.co.uk/boxford/index.html

John

Offline Darren

  • Madmodder Committee
  • Hero Member
  • *****
  • Posts: 3795
  • N/Wales
Re: Finishing problems
« Reply #14 on: November 12, 2008, 03:56:05 PM »
John,

I can see you are a man with a passion/obsession for tools. How can I say no to your offer !!

Wonderful, the "dinky" may stay with me yet,

Think I'd better I'll 'ave a little chat with Ralph about these "rules" of yours.. :hammer:

Darren
You will find it a distinct help… if you know and look as if you know what you are doing. (IRS training manual)

Online Brass_Machine

  • Administrator
  • Hero Member
  • *****
  • Posts: 5504
  • Country: us
Re: Finishing problems
« Reply #15 on: November 12, 2008, 10:17:14 PM »
Darren,

You are a lucky man. Bogs is one of the nicest guys in my hobby circle. I would love to live close by to go for a visit and coffee. Alas, I have an ocean to cross first. However, the day will come when he and Ralph will have to put up with me coming for a visit.

Take him up on his offer!

Eric
Science is fun.

We're all mad here. I'm mad. You're mad.

Offline Darren

  • Madmodder Committee
  • Hero Member
  • *****
  • Posts: 3795
  • N/Wales
Re: Finishing problems
« Reply #16 on: November 13, 2008, 07:07:43 AM »
Darren,

Bogs is one of the nicest guys in my hobby circle.
Eric

I'm starting to realise this, and I suspect many others here fall into a similar category.

I went to my local scrappy to see if I could find any suitable material for lathe work, I was told by the owner  "sure have a good look around and take what you want mate"

My world has suddenly become a nicer place !!

Darren

You will find it a distinct help… if you know and look as if you know what you are doing. (IRS training manual)

Offline CrewCab

  • Madmodder Committee
  • Hero Member
  • *****
  • Posts: 851
Re: Finishing problems
« Reply #17 on: November 13, 2008, 09:24:41 AM »
In the UK, you can't go far wrong with one of the UD boxford range, preferably the AUD.

Funnily enough John and I had a similar conversation a few months back ................. and .........  lo and behold ...........  look what followed me home ........... 



Before that I was using a Chester 9" x 20" which is a nice little machine, but to be fair the Boxford does have an edge, mainly due to build quality and mass, it treats CRS like the 9 x 20 deals with aluminium.

Dave .............. aka .............. CC 
« Last Edit: November 13, 2008, 10:06:16 AM by CrewCab »

Offline Darren

  • Madmodder Committee
  • Hero Member
  • *****
  • Posts: 3795
  • N/Wales
Re: Finishing problems
« Reply #18 on: November 13, 2008, 10:01:26 AM »
That looks good Dave, a lot of people really favor these Boxfords from what I can tell.

Alas I have an ambitious project in mind for the future in that I wish to turn a new 12" or even 13" platter for my record player.
On those lines I'm thinking a Colchester Student for example, I also wish to turn 30mm S bars up to around 300 or 400mm long and drill and tap the ends.
I can do the last bit on my S&B if the new lathe isn't able.

I know from experience, that I want the next lathe purchase to be my last, famous last words.


Thanks John, I will speak to Ralph hopefully face to face sometime. I have been playing with metal for a long time.
It's the machining/engineering that's new to me...loving it though.

Did you see the link to my now very old web site? http://homepage.ntlworld.com/darren.dean/index.htm

You will find it a distinct help… if you know and look as if you know what you are doing. (IRS training manual)

Online Brass_Machine

  • Administrator
  • Hero Member
  • *****
  • Posts: 5504
  • Country: us
Re: Finishing problems
« Reply #19 on: November 13, 2008, 10:37:55 AM »
Darren,

Both the GSXR and the locost fit in well here (yes I have the build a sportscar book...). I am very heavily into bikes and cars as well. Look about the forum and you will see my CF stands. Both projects will fit in here, do up some posts!

Eric
Science is fun.

We're all mad here. I'm mad. You're mad.

Offline Darren

  • Madmodder Committee
  • Hero Member
  • *****
  • Posts: 3795
  • N/Wales
Re: Finishing problems
« Reply #20 on: November 13, 2008, 09:16:24 PM »
Hi Eric,

Those were some time ago now. I spent 4 years working on that bike, every nut and bolt etc. The engine was bored, gas flowed, dyna jetted etc and was a stonker.
160 two up no problem.... There was very little of the original bike by the end, I'd fettled with just about everything. Gearbox, clutch, suspension frame bodywork and painted it more than a few times !!

The Locost was never finished, sadly due to personal circumstances I had to put all my belongings onto storage for a year or so until
some lowlife emptied the lot, my whole life...gone in one stroke....bike, car, tools the lot.

Anyway, life moves on dunit, that was a while ago now and after a long absence I'm slowly putting a workshop back together.
Different goals, same lunatic at the wheel.... ;D
You will find it a distinct help… if you know and look as if you know what you are doing. (IRS training manual)

Online Brass_Machine

  • Administrator
  • Hero Member
  • *****
  • Posts: 5504
  • Country: us
Re: Finishing problems
« Reply #21 on: November 13, 2008, 10:08:48 PM »
Locosts are pretty cool. I am working on a locost inspired 3 wheeler powered by a sporting V-twin. Right now it is in the very early phases. Only exists in my head and a few bits here and there in my CAD software. I will probably start it next summer as long as I find a new job and get my finances straight first.

Sorry to here about the low life. Thieves should be hung.

Eric
Science is fun.

We're all mad here. I'm mad. You're mad.

Offline Divided he ad

  • WARNING: LIKES SHINEY THINGS
  • The Collective
  • Hero Member
  • *****
  • Posts: 1950
  • Country: gb
  • Between Chester, Wrexham, ruthin & Holywell :-)
Re: Finishing problems
« Reply #22 on: November 14, 2008, 04:29:16 PM »
Quote
Thieves should be hung......
Edit.... You missed "Drawn and Quartered" !! I fully concur!


 (IMO)


Ralph.
I know what I know and need to know more!!!

Offline CrewCab

  • Madmodder Committee
  • Hero Member
  • *****
  • Posts: 851
Re: Finishing problems
« Reply #23 on: November 14, 2008, 04:39:22 PM »
Can I add "needle at birth", just a personal opinion of course

CC  >:(

bogstandard

  • Guest
Re: Finishing problems
« Reply #24 on: November 14, 2008, 06:12:55 PM »
You lot would make it to easy for them.

Meathook thru the dangly bits, then a brick hung on the end, 3" above the ground.

Oh, I forgot, public branding on the forehead with a big letter T as well.

That is a bit better than sending them on safari.

Offline Darren

  • Madmodder Committee
  • Hero Member
  • *****
  • Posts: 3795
  • N/Wales
Re: Finishing problems
« Reply #25 on: November 14, 2008, 06:23:23 PM »
That is a bit better than sending them on safari.

Why do They do that? Hardly any incentive for the rest of them is it.

Or perhaps it is, pay once, pay twice.....
You will find it a distinct help… if you know and look as if you know what you are doing. (IRS training manual)

Offline Darren

  • Madmodder Committee
  • Hero Member
  • *****
  • Posts: 3795
  • N/Wales
Re: Finishing problems
« Reply #26 on: November 16, 2008, 05:35:16 AM »
Bought some Gunk (engine cleaner) is a spray can yesterday from the "local" market stall. (and a set of 5 HSS slitting saws, I'm sure they'll come in handy at some point)

So last night I cleaned the 7x12 down a bit. Took the back guard off to get better access at the read bedway and to my surprise there was loads of paint on the underside.
Thinking that this is what I may have been measuring I set about cleaning it off. Some of it was pretty thick too, I had to carve it off carefully in layers. It didn't cover the whole width, but it might have been catching the carriageway along its travel.

Alas no improvement. Now I have better access to that area I can measure it more accurately. I'm getting up to 7thou difference from one end of the bed to the other, with about 3.5thou over the used section of the bed.

Sadly, I think this bed needs some surgery, otherwise I'm flogging a dead horse here.

John if your kind offer is still open we'll have to form a plan .......I'll pm you later if you don't mind

Regards
Darren
« Last Edit: November 18, 2008, 01:18:36 AM by Darren »
You will find it a distinct help… if you know and look as if you know what you are doing. (IRS training manual)

bogstandard

  • Guest
Re: Finishing problems
« Reply #27 on: November 16, 2008, 06:35:33 AM »
No Problems Darren.

John

Offline rleete

  • Madmodder Committee
  • Hero Member
  • *****
  • Posts: 534
  • Country: us
Re: Finishing problems
« Reply #28 on: December 12, 2008, 09:12:33 AM »
Darren,

Any resolution on this?  My lathe (Homier 7 x 12) is doing the same thing, and I'm going nuts trying to fix it.  This happens all the time - not just when using the leadscrew, but in all turning work.  I initially thought it was the headstock bearings, but I tightened them up and it didn't help.

Gibs & half nuts have been adjusted over and over.  I improved backlash, and tightened it up a bit, but the "turning marks" are still visible on parts.  It means a lot of extra work finishing parts, and I have to account for more material removal (sanding/polishing) and it's causing me to tear my already thinning hair out!

Anyone?
Creating scrap, one part at a time

Offline Darren

  • Madmodder Committee
  • Hero Member
  • *****
  • Posts: 3795
  • N/Wales
Re: Finishing problems
« Reply #29 on: December 12, 2008, 09:35:16 AM »
Hi rleete ?

Nothing done as yet I don't believe, but there is no hurry on this as I have another lathe to use. I'm not personally the one being brave with the bed work  :bugeye:
But when the time comes it will be cataloged on these very pages. Should be sometime soon so keep an eye out.

On the head bearings. The standards are plain roller bearings, I changed mine with tapered types when it was nearly new in an attempt to solve this problem thinking it might be the cause.
It wasn't, made no difference to the finish.

I have to agree with you this problem really spoils this otherwise very capable little lathe.

BTW, welcome to the forum, please let us know what you make and interests are. I'm guessing you are in the US?

Darren
« Last Edit: December 12, 2008, 09:41:42 AM by Darren »
You will find it a distinct help… if you know and look as if you know what you are doing. (IRS training manual)

Offline rleete

  • Madmodder Committee
  • Hero Member
  • *****
  • Posts: 534
  • Country: us
Re: Finishing problems
« Reply #30 on: December 12, 2008, 09:45:05 AM »
Yes, in the US.  Rochester, NY to be exact.

I'm a mechanical designer (tooling & fixtures, mostly), and a novice machinist.  I have a HF micro mill and the lathe.  My current projects are in the model steam engines category.  I'm also somewhat of a car nut.

I found this forum several weeks ago, and just joined H M E M, so decided to sign up here as well.
Creating scrap, one part at a time

Offline Bernd

  • Madmodder Committee
  • Hero Member
  • *****
  • Posts: 3688
  • Country: us
  • 1915 C Cab
    • Kingstone Model Works
Re: Finishing problems
« Reply #31 on: December 12, 2008, 10:13:11 AM »
Yes, in the US.  Rochester, NY to be exact.

Hey rleete I'm 20 miles south of you, West Bloomfield to be exact.

Bernd
Route of the Black Diamonds

Offline rleete

  • Madmodder Committee
  • Hero Member
  • *****
  • Posts: 534
  • Country: us
Re: Finishing problems
« Reply #32 on: December 12, 2008, 10:41:56 AM »
Hi Bernd.  Nice website.  I see you have the same PM research engine I have.  Buying that kit (eBay) is what got me started on this whole exercise.

I have a single vertical wobbler in process, as well as parts for several more.  I figured I had better get some machining experience before tackling the PM kit, so as to not mess it up.
Creating scrap, one part at a time

Offline Bernd

  • Madmodder Committee
  • Hero Member
  • *****
  • Posts: 3688
  • Country: us
  • 1915 C Cab
    • Kingstone Model Works
Re: Finishing problems
« Reply #33 on: December 12, 2008, 10:46:53 AM »
Great.

I'm extending an invite if you if you want to see the shop personally.  :thumbup:

Bernd
Route of the Black Diamonds

Offline rleete

  • Madmodder Committee
  • Hero Member
  • *****
  • Posts: 534
  • Country: us
Re: Finishing problems
« Reply #34 on: December 12, 2008, 11:03:56 AM »
Thanks.  Maybe the week after Christmas?  I have a couple of weeks vacation, and I plan on spending most of it in the shop.
Creating scrap, one part at a time

Offline Bernd

  • Madmodder Committee
  • Hero Member
  • *****
  • Posts: 3688
  • Country: us
  • 1915 C Cab
    • Kingstone Model Works
Re: Finishing problems
« Reply #35 on: December 12, 2008, 12:37:38 PM »
No problem. I'm retired, wife says retarded, but what does she know  :D so any time of day would be fine by me. PM me with a time of your convenice and I'll give you directions on how to get here.

Bernd
Route of the Black Diamonds

Offline sbwhart

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 3530
  • Country: gb
  • Smile, Be Happy, Have Fun and Rock Until you Drop
Re: Finishing problems
« Reply #36 on: December 12, 2008, 12:49:57 PM »
Hi Guys

I've got a similar surface finish problem with my Chester 3 in 1. My little grey cells  : :scratch: have been working on the problem on and off for the last couple of years. I was wundering if anyone has checked their jib strips out for straightness ?, the guy who runs the mini lathe and mini mill site recomends lapping them flat, as anyone tried this ?. I've got a job in machine at the moment as soon as its finished I'm going to check it out, Johns got a surface grinder and lives a short walk from my home so hopefully he'll let me use it on my jib strips :thumbup:

Have Fun

Stew
A little bit of clearance never got in the road
 :wave:

Location:- Crewe Cheshire

bogstandard

  • Guest
Re: Finishing problems
« Reply #37 on: December 12, 2008, 01:35:24 PM »
I will be starting Darrens lathe soon, and I will do a write up in this post. I can't guarantee it will solve the problem, but it definitely won't harm the lathe, and it will also show if this is the root of the problem for Darren.

Basically I will be skimming the underside of each side of the bed rails to get them parallel (there is a rather large sticky out bit underneath each one that is doing the lathe no favours, set the jibs to the tight spot, and anywhere else the saddle wobbles about), and then fitting tapered jib strips in brass or bronze (depends on what I can get my hands on).

All will be revealed.

John

Offline rleete

  • Madmodder Committee
  • Hero Member
  • *****
  • Posts: 534
  • Country: us
Re: Finishing problems
« Reply #38 on: December 12, 2008, 01:58:12 PM »
I talked to the diamond machinists at work today about this.  Recommendations were that it was the tool and the ways.  Oh, and the operator.  Something about the nut at the wheels being off...  :)

I was told that the finish cut should be at a faster machine speed, and that the tool should have a large radius.  We manufacture tooling for lenses, and some of the ones we do are plain mirrors - called "planos" in the biz.  The tools they use are large radius diamonds (large for them being in the .25"-.31" range) on hard copper.  When the part is done, you can't tell it's been turned, but is a circular mirror of up to 24" diameter.  Plus or minus .0005 is wide open tolerances for these guys.

As to the ways, they said they are too lose, and when I'm taking larger cuts to get to the finished diameter, the wavyness is the result of uneven pressure on the tool against the work.  It sort of work hardens the surface, so that the finihed cut can't remove all of it evenly.  So lighter cuts on the turning if I can't tighten up the ways more.  Lapping the gibs should help, but I've been avoiding it.  It was also recommended that I back off the leadscrew nuts before tightening the ways, as that may be influencing the way the slide fits on the bed.

So, I'll try tearing down the machine and lapping the gibs.  Then reassemble, paying particular attention to get the best adjustment at the point where I do the most turning (near the headstock), and then worry about backlash.  I'll post results when I get it dialed in.
Creating scrap, one part at a time

Offline Darren

  • Madmodder Committee
  • Hero Member
  • *****
  • Posts: 3795
  • N/Wales
Re: Finishing problems
« Reply #39 on: December 12, 2008, 02:59:43 PM »
Ok,
I'm not disputing what you say above but the first thing I would advise is to accurately measure the bed ways for even thickness and parallelism.

My lathe that show the same symptoms as yours was way out. The bed was thicker in the middle than at either end. This meant that the gibs could not be adjusted properly.
It certainly needed a little more than hand lapping, I think lapping is for ways that are almost correct and just need a bit of fine tuning to finish them off.

I also tried finishing at different speeds, different tooling etc, non of it made any difference. Besides, you can't really up the speed for larger diameter work so better to find the cause to see if you can cure than to try and work around it.

You will find it a distinct help… if you know and look as if you know what you are doing. (IRS training manual)

Offline rleete

  • Madmodder Committee
  • Hero Member
  • *****
  • Posts: 534
  • Country: us
Re: Finishing problems
« Reply #40 on: December 12, 2008, 04:50:44 PM »
Just finished tearing down the compound slide.  The gibs are poorly machined, as most would expect.  But, the damn things are bent!  Both are warped 1/4 from the end, like they got caught in something.  I straightened them both, easily.  A bit of sanding on the surface trued them up quite well.  I can't see how that won't improve things, and I'm very surprised I didn't see it when I disassembled for cleaning.  I also retapped the screw holes, as one set screw felt like it was binding.  It feels much smoother now.

The ways are flat (at least on top), from my inspection with a straight edge.  Thickness appears uniform, but there is some paint on the bottom side I scraped away.  Also a couple of minor burrs, which didn't look to affect anything, but I stoned them off anyway.  I'll keep going and let you all know how it turns out.
Creating scrap, one part at a time

Offline Darren

  • Madmodder Committee
  • Hero Member
  • *****
  • Posts: 3795
  • N/Wales
Re: Finishing problems
« Reply #41 on: December 12, 2008, 04:54:42 PM »
Yes please do, tell us anything you find that seems out of place.....

I know the gibs are not brill, nothing more than a bit of steel chopped of a length of bar,
but bent  :jaw:
You will find it a distinct help… if you know and look as if you know what you are doing. (IRS training manual)