Stiffening A Mini Lathe Bed

petcnc

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I have a mini lathe 7X12 under the name “Clarke” that I have bought from UK some 5 years ago.

Lathe_On_wooden_table1.jpg


As you can see, the lathe sits on a wooden table without any other support and rests on 4 rubber feet (that you cannot see).

It behaved ok so far without any problems having very light duties though.

As I sought a better lathe out of my Clarke, I made a few improvements to gain in accuracy.

To name a few of the improvements (That you can see to other posts if you scroll further down) I changed the bearings with tapered roller ones, I lowered the topslide to be able to use 12mm (1/2”) tools, I made a number of changes to the tailstock and bought a pair of 5” chucks to replace the hectic 3” ones the lathe came with.

PC300377.JPG


Although I made all these changes and adjust every aspect I could, the lathe remained very “delicate” and even my breath could ruin it’s accuracy.


The best I managed to achieve was to cut a bar, supported between centers, achieving an accuracy of 0,01mm, end to end, to a length of 250mm (12”) with very light cuts. Most people would be happy with these results but I was looking for something better than this.

Moreover, what puzzled me was the lathe’s tendency to ruin this accuracy when I tried a cut deeper than 0,25 mm (0.01”)! I knew I had to do something about it but for years I was leaving it for “later” and this later took 5 years to come!

Seeking info to the net, I found that the weak point of the mini lathe is the bed and its tendency to bent under stress. This seems to be the main cause of its poor accuracy results. Having set the TDI at the end of a bar supported on the chuck I tried to twist the lathe by pushing the head and pulling the tailstock. To my surprise the TDI moved 0.5 mm (0.2”). It was time to do something about it to reduce this flexibility.

I have some old steel beams 80X30mm having a thickness of 3mm.

Beams.jpg


I thought that If I weld 2 of them together I could make a base strong enough to bolt my lathe on it to make it less flexible.

base1.jpg



The idea was to bolt the lathe on it to give extra rigidity to the bed

LatheWithBase.jpg



So I cut them weld them drill them and put the lathe on it.

BaseFitted.jpg


I used long bolts to secure the lathe on the base.

long bolts1.jpg


And an extra nut between lathe and base to level the bed.

Adjusting.jpg


Lathe fits beautifully on the base and I gained the extra rigidity I wanted.


Now it moves only 0.15mm when I try to twist the bed.


Final view.jpg


Thank you for reading


Petros
 
Last edited:
Just above the last pic above he says he now sees .15mm of movement.
 
Very interesting....Since I am going to be starting a bed extension on my mini-lathe maybe I will need something thicker than what I was going to use for the base. Will have to think about this for a bit. I will be posting pics as I go along. Right now I need to clean up both beds and check some dimensions. So far the dimensions I checked look good for the donor bed to work.
 
Weldments can be a bit unstable. I'd opt for a piece of 3/4" (19mm) plate, blanchard ground. :)

Tony: That is exactly what I did with my Micro Mark 7x16, but didn't want to suggest it as it is a rather pricey solution. Worked really, really well though. :)
 
I have 70% better results now. Before the max movement was 0,5mm now is 0,15.
Well I would like it to be zero but I think I can live with it...

Petros
I have 70% better results now. Before the max movement was 0,5mm now is 0,15.
Well I would like it to be zero but I think I can live with it...

Petros
Yes, I saw that, but what are the results now in accuracy on the work?
 
Yes, I saw that, but what are the results now in accuracy on the work?

Bob I see what you mean! I tried a cut 0.35mm to a bar today. Accuracy is 0.01 as expected to be but...
My mini lathe revealed another weak spot! Motor power. As the motor is just 300W it complained when I was cutting at 0.35mm.
To be honest I did not dare to go deeper to test the accuracy further. I might try it after an extra slow feed speed modification I have in the "to do" list.

Petros
 
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