Colchester student run out

This topic has 6 replies, 5 voices, and was last updated 15 August 2012 at 16:40 by Russell Eberhardt.

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12 August 2012 at 17:48 #96234
ross keeling
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@rosskeeling18140
I have gone to a bit of expense and had my square head Student lathe fitted with a new chuck, new DRO and give the machine a basic going over.

Yesterday I had to turn a new shaft 8" long for a set of pedals (I work on vintage cars) and it had about a 20 thou run out once machined from chuck (normal jaws) to tail stock.

The material was a piece of 1" EN8 and turned at 420 or 440 rpm (red setting) down to 7/8" and was 20 thou out, I then run the machine at around 550 rpm the next speed up and it took about another 2 thou off. The bar was supported with a tail stock steady.

My question is can the bed be worn to that amount or could some thing be slightly out of alignment?

Any pointers would be really help full.
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12 August 2012 at 17:48 #22177
ross keeling
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@rosskeeling18140
14 August 2012 at 15:45 #96317
John McNamara
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@johnmcnamara74883
Hi Ross

Welcome Aboard

You turned a nice taper!

There are many possible causes, If the lathe is in good condition and you used the tail stock with a centre located in a centre hole drilled in the end of the bar to turn the piece then I suspect the tail stock is the problem…. it may be off centre. You may need to adjust it, and do test turnings on scrap until it is right.

When I get a problem I cannot fix I find that Google using a simple English like sentence will normally provide a quick answer. I tried the sentence below and found a number of articles dealing with your problem.

Google the following
lathe will not turn parallel

I am intrigued what does "420 or 440 rpm (red setting)" mean?
Normally speed is calculated by various tables. The material to be turned, the cutting tool type, the stiffness of the machine, the stiffness of the work piece, and with or without coolant, among others all affect the result.

And even after consulting the tables you may have to adjust the speed and feed for your particular situation, It is part science part art.

Google the following
Lathe speeds and feeds turning

Cheers

John
14 August 2012 at 16:48 #96323
ronan walsh
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@ronanwalsh98054
Is the machine sitting level and straight on the floor Eg no twist along the bed ? I have a colchester too and have looked into alignment, you can offset the tailstock left and right for taper turning and maybe this has been done and not returned to centre ? A test bar with morse taper to suit your tailstock are available for you to check alignment.

on my lathe (a master 2500) the headstock is also moveable left and right , if a length of 1" ground steel bar is held in the four jaw chuck and clocked up central , a dti can be held in the tool post and run along the length of the bar to test for misalignment.

Just a few ideas , i am sure there will be more experienced people along who will explain this better and better ideas than myself.
14 August 2012 at 19:47 #96335
ross keeling
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@rosskeeling18140
On the student the chuck speeds are colour coded and the red setting I was using was 410 rpm.

I have never had any tuition on a lathe so I am learning each time I use the machine! I think a few hours on google will help.

The lathe is level as I did this job myself and I think adjustment of the tail stock and turning a few test pieces will be a good start.
14 August 2012 at 21:12 #96342
Tony Pratt 1
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@tonypratt1
Try cutting a piece of 1" Mild Steel x 6" long bar unsupported using a sharp HSS tool to see if the lathe itself will cut parallel.

Tony
15 August 2012 at 16:40 #96390
Russell Eberhardt
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@russelleberhardt48058
It sounds as if the tailstock is set over. Put a centre in the tailstock, one in the headstock and bring them together. They should line up exactly. You can lightly pinch a razor blade between the two and adjust the tailstock untill it sits at right anles to the lathe axis.

If that doesn't work Google for "Rollie's Dad's Method" to get the lathe properly leveled

Russell
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