Author Topic: Sorting out accuracy on my Mill/Lathe  (Read 12303 times)

Offline djh82uk

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Sorting out accuracy on my Mill/Lathe
« on: November 28, 2009, 09:00:31 PM »
Hi Guys

Inspired by posts on here (most notably fixing darrens lathe) I have decided to check and service my machines.  Some of you may have seen from my other posts that I am in the market for a larger mill & lathe, so I converted my Taig mill from CNC back to manual.  When I got the mill, I immediatley converted it to cnc (after playing with the handwheels for a while whilst going oooooh), so in short I have never manually milled, and thought that I should so that I had a better odea of what I want in a new mill.

Well I got it back to manual and found quite a bit of backlash on the Y axis (moves the table to/from the column?),  I measured it as 3 thou.  I measured it by putting my dti up against the table, and moved the wheel to 0 one way, and then turned the handle very slowly until the needle budgedm hand wheel registered a movement of 3 thou before the needle moved.  This was the only way I could think to measure it as the machine is imperial and my DTi in metric.

Now I have a confession to make, I have not stripped this machine back down since it was first converted to cnc, the gibs were out, I had backlash and there was oily gunk everywhere.  So i thought I would stip it down.

It is currently in pieces being cleaned up.


Now as for my lathe, after reading bogs log of fixing darrens lathe I though "oh cr*p" as I have always struggled to get a decent finish, nothing a bit of W&D doesn't fix, and sometimes I do get a nice finish, normally it has ridges in it (I always thought that I just did not have a fine enough feed), so I want to set the lathe up as if I just bought it 2nd hand., so what do I check, and how do I check it?

Starting with the carriage bed, the only way I could think of was to mount the dti stand on the cross slide, the dti arm on the bed, and move the carriage back and for, I get a max offset of 0.03mm, is that 1 thou or 11 thou?.

Obviously I need to also check the chuck & tailstock, tailstock I am fairly sure is out but I don;t know how to check it not having a test bar or co-axial dial indicator.

I have some very straight looking steel rods out of a desktop scanner, but doubt they were made to the correct tolerances.  And they are obviously an unknown.

Any advice?

I uploaded a bunch of pics here until I can find a better batch image resizer for linux:

http://pomme-bleu.co.uk/wedding/categories.php?cat_id=3&page=1

Offline djh82uk

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Re: Sorting out accuracy on my Mill/Lathe
« Reply #1 on: November 28, 2009, 09:59:13 PM »
Hmm, apparently the backlash from the factory is normally 0.0015 to 0.003 inch, still seems a fair bit to me tho, and I don't like being at the higher end of the scale

DJH

tumutbound

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Re: Sorting out accuracy on my Mill/Lathe
« Reply #2 on: November 28, 2009, 10:02:56 PM »

I uploaded a bunch of pics here until I can find a better batch image resizer for linux:


For Linux, install ImageMagick and use the mogrify command.

Offline djh82uk

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Re: Sorting out accuracy on my Mill/Lathe
« Reply #3 on: November 28, 2009, 10:14:18 PM »
Yeh I have imagemagick on the machine but it makes all the images blocky, eve after fiddling with settings.  I have GDimage on my webserver and that works fine for now but am using that php page until i sort it out in my own machine, re-compiling imagemagick throws up a GCC error so I must have a conflict somewhere

Offline djh82uk

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Re: Sorting out accuracy on my Mill/Lathe
« Reply #4 on: November 28, 2009, 10:21:28 PM »
Ok, just tried testing my lathe chuck, with the dti on the outer body of the chuck I get a movement of 0.03mm or 1.1 thou, is that within normal expected tolerance for a mini-lathe?

Russel

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Re: Sorting out accuracy on my Mill/Lathe
« Reply #5 on: November 28, 2009, 11:02:12 PM »
Sherline suggests that with their equipment .003" to .005" is normal for manual operation [edit: for leadscrew backlash. I just noticed you were talking about the chuck.] CNC usually requires .003" or less if I understand the recommendations correctly. I've kept my equipment between 3 and 5 thousandths with good results. Of course, I always approach a setting turning the hand wheels the same direction to account for backlash.

Fixing Darrens lathe made a big impression on me as well. Since then, I've gone over my machine tools with a fine tool comb. I also ripped apart the bench I use them on and built it up solid and square, as well as using a composite quartz counter top remnant under the machine tools as a good flat surface. I've also made it a habit to always carefully clean and oil the ways when I am done for the day.
« Last Edit: November 28, 2009, 11:04:15 PM by Russel »

Offline jim

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Re: Sorting out accuracy on my Mill/Lathe
« Reply #6 on: November 29, 2009, 12:49:52 AM »
i just put some 1" bar in the chuck on the C3 i've just bought, turned about 6" length and checked for taper, much to my horror it was about 6 thou. soon got it down to a much more acceptable 1 thou over 6" :thumbup:
if i'd thought it through, i'd have never tried it

bogstandard

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Re: Sorting out accuracy on my Mill/Lathe
« Reply #7 on: November 29, 2009, 04:33:38 AM »
Gents, it is very difficult trying to suggest 'fixes' for individual machines, because they are all different in some way.

So really it is a matter of you looking at how the adjustments are made, and spending time tweaking until they are spot on or within your acceptable limits.

I have noticed that a few of you are getting confused by the metric/imperial way of thinking, and of course if you are used to working in just one, it can be difficult working in the other.

I am lucky that I can interchange between the two automatically and can also think in both, but for small figures the decimal point in either can be confusing. So here are a few easy conversions, that if you can remember them, will help when working with the 'other one'.

0.01mm roughly equals 0.0005" (half a thou)

0.025mm is 0.001" (1 thou)

0.05mm is 0.002" (2 thou)

0.1mm is 0.004" (4 thou)

So coming from the other way

0.040" (40 thou) is 1.0mm

0.010" (10 thou) is 0.25mm

0.005" (5 thou) is 0.125mm

These are close enough guesstimates in what you are working with.
I know it is difficult sometimes being able to afford measuring intruments, but if at all possible, try to use instruments that are in the same standard as the machine you are working on.

And don't forget, the correct lube for the job. It does make a big difference to how a machine runs and operates. That is why there are so many on the market, they all have a different job to do.

Have you started to notice that the machine isn't cutting the way it normally does, then ask yourself, when was the last time I gave it a drink?


Bogs

Offline djh82uk

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Re: Sorting out accuracy on my Mill/Lathe
« Reply #8 on: November 29, 2009, 09:12:07 AM »
Thanks guys

Im trying to decide wether to leave it or try and improve it a smidge for the mill.  Need to find a type of oil to use aswell,


The lathe however, I am still looking for ways to measure things, and wether 1 thou runout on the chuck is ok.

I did just notice however that the 0.03m deflection on th ebed was caused by the carriage being able to be lifted up at the back by about 20thou.

So thats gotta be sorted first, im presuming at this moment that the gib screws have loosened


DJH

Offline websterz

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Re: Sorting out accuracy on my Mill/Lathe
« Reply #9 on: November 29, 2009, 11:01:16 AM »
...I did just notice however that the 0.03m deflection on th ebed was caused by the carriage being able to be lifted up at the back by about 20thou.

So thats gotta be sorted first, im presuming at this moment that the gib screws have loosened


DJH

That is definitely the place to start! Adding a carriage lock will help as well. On facing cuts you can lock it down solid, on turning ops you can just snug it up a bit to help hold things down. Tapered gibs are of course the ultimate solution.  :proj:
"In the 60's, people took acid to make the world weird.  Now the world is weird and people take Prozac to make it normal."
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Offline djh82uk

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Re: Sorting out accuracy on my Mill/Lathe
« Reply #10 on: November 29, 2009, 11:23:35 AM »
Well Ive been working on both machines today, I did not have the confidence to start adjusting the taig, I have 3 thou backlash on the Y, 2 thou on the X and 1/2 a thou on the Z, I did clean everyything completley stripping down the X & Y and relubed, adjusted gibs etc.  Still need to clean & lube the Z.



As for the lathe, I was looking on mini-lathe.org.uk and read about how his chuck  was out by 15 thou, and when he got it to 2 thou he was very happy, so I guess i should be reasonably ok with 1 thou runout for now.

As for the saddle, I took the splashback off and got to work, there does not seem to be any brass gibs, just 2 cap screws, 2 lock screws (grub screws & nuts) and a brittle piece of steel.


Sooo, one of the cap screws was so loose it could be turned by hand, so I set about getting them to the same tightness, and then started tightening the locking screws, the saddle now is a bit tighter to turn, and probably would tire my arm out if I had to move it three lengths one after another, but....

After puting the dti on the bed and the arm on the carriage, I can try and lift the saddle and the dti deflects by about 1/4 of an increment which is roughy 0.0025mm, which I expect is ok for now, also adjusted the backlash screws for the cross-slide and and got that nice and smooth with minimal backlash, the compound was ok from last time I adjusted.


I also took the time to completley clean and lube everything.

I tried a test cut, pic below, not perfect but better, the dis-coloration is my oily fingerprint btw




DJH

Offline djh82uk

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Re: Sorting out accuracy on my Mill/Lathe
« Reply #11 on: November 29, 2009, 11:40:53 AM »
Still not 100% happy with the finish, or is this about what I can expect?  I can just about see lines in the workpiece, but can just about feel them if I run my nail along it, Should the workpiece always need finishing afterwards?  Im not sure if it is the lathe or the tooling, I have carbide with (changeable tips) & TCT brazed, both give a similar finish, or should I be using HSS? (I have never properly tried grinding my own tools but need to learn, should I be using a slightly rounding tip for finishing?


My next few tasks are to tram my Mill (desperatley needs doing, but never done it before), not sure how to be able to check how far out it is.

Center my tailstock & to check runout on my mill spindle

Offline NickG

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Re: Sorting out accuracy on my Mill/Lathe
« Reply #12 on: December 01, 2009, 08:23:40 AM »
DJH,

that looks a really good finish on the pic to me. it doesn't really matter about run out on the chuck body it's on piece of metal gripped in the jaws that counts. 0.001" is good for a s/c chuck I would say.

nick
Location: County Durham (North East England)

Offline djh82uk

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Re: Sorting out accuracy on my Mill/Lathe
« Reply #13 on: December 01, 2009, 02:09:48 PM »
Hiya

I don't use a S/C chuck as the only 4" chuck I have is independant, it's ok tho.

I think i need to look into tooling, could someome post up a pic of the tool they use for a nice finish on aluminium?

Im not sure a carbide tip is the way to go?

Should I have a slightly rounded tip?

I also tried cutting mild steel but got a bad finish with carbide, I need to figure out tooling next i think, I just use whatever i have at the time which is obviously not the way to go.

I guess I also need to learn to grind my own

DJH

Offline Darren

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Re: Sorting out accuracy on my Mill/Lathe
« Reply #14 on: December 01, 2009, 02:12:36 PM »
I've never had any trouble using carbide on aluminium, brazed, tips coated or otherwise.

But I know people swear by HSS.
You will find it a distinct help… if you know and look as if you know what you are doing. (IRS training manual)

Offline djh82uk

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Re: Sorting out accuracy on my Mill/Lathe
« Reply #15 on: December 01, 2009, 02:24:05 PM »
I found some old blunt hss bit that I may regrind, just need to make a grinding rest as I don't trust the one that came with it (crappy 9" bench grinder)

DJH

Offline Darren

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Re: Sorting out accuracy on my Mill/Lathe
« Reply #16 on: December 01, 2009, 02:27:40 PM »
You are being too fussy, grind it freehand .... nothing is critical, just get it close.  :thumbup:
You will find it a distinct help… if you know and look as if you know what you are doing. (IRS training manual)

Offline djh82uk

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Re: Sorting out accuracy on my Mill/Lathe
« Reply #17 on: December 01, 2009, 03:20:23 PM »
well I just tried grinding an existing tool, just sharpened it a bit and added bit of a radius to the cutting point,

Here is the piece after a light cut, the material is bright mild steel:



And after some rough sanding:



And then some wet sanding:




And the finished item after a go with a polishing wheel:





Im fairly happy with that, may try some aluminium next


DJH

Offline djh82uk

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Re: Sorting out accuracy on my Mill/Lathe
« Reply #18 on: December 01, 2009, 03:42:48 PM »
also just checked runout on the shiny part and I get about 1/10th of an increment on the dti, which equates to about 0.001mm, is that 0.3 thou?

I guess I should try it on a non polished piece, but just after cutting, but would'nt the little ridges affect the reading a bit?

Either way I guess I don;t have chronic runout

Thanks

DJH

Offline sbwhart

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Re: Sorting out accuracy on my Mill/Lathe
« Reply #19 on: December 01, 2009, 03:57:31 PM »
DJH

Thats not too bad, I wouldn't worry too much about that finish ther's a lot of factors that are out of your control that can effect finish, the material for one thing ther's lot of grades of mild steel some are s**t to machine and some are great and give a real good finish, some grades of steel are very dificult to machine, you'l learn to recognise them in time.

You want to try and keep the amount of polishing down to a minimum, try and get the best finish you can off your machine and only polish where its needed.

Have fun

Stew

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Offline NickG

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Re: Sorting out accuracy on my Mill/Lathe
« Reply #20 on: December 02, 2009, 03:35:08 AM »
DJH,

looks good to me. For aluminium, if using HSS which I do at the moment (have asked father christmas for some carbide tipped tools to try though!) you need a high rake angle becuase the metal is soft and swarf comes off in long strings. Most of the stuff I've seen say about 40 degrees top rake for aluminium, about 20 for steel and about 2 for brass / cast iron. The other angles are just to clear the work to ensure no rubbing. Of course getting it on centre height is critical, there are other posts on here to show how to do that. I usually try to put a very small radius on because most stuff we do requires getting the tool into corners, unless I specifically need a radius to suit a certain feature. The smaller radius also gives less rubbing of the workpiece but go too sharp and you will get a ridged finish, you need something on there.

Nick
Location: County Durham (North East England)