Author Topic: Mini lathe compound handle bearings  (Read 8851 times)

Offline loply

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Mini lathe compound handle bearings
« on: June 12, 2011, 07:03:53 PM »
Hi folks,

Just finished the first part I've made on my lathe! Quite happy with the result.

The compound handle on my lathe was made very badly in that the two dials were not faced properly (or bored properly, depending on how you look at it) and as such there was always a lot of friction coming from the handle, and also the further in you wound the slide the tighter the handle got because the shaft was not concentric with the thread it rides in...

Also, by virtue of the design of the system, the more resistance there is to movement of the compound slide, the more FRICTION you get in the handle mechanism. That's to say, if there is resistance to the slide moving because of tight gibs, the two dials of the handle exert more friction on each other, meaning you get an exponential increase in difficulty turning the little handle when you make the gibs tighter.

Anyway! I designed a system which aimed to solve a few problems:

1) Bigger handle
2) Rotating outer tube on handle
3) Thrust bearings to carry both inwards and outwards thrust
4) Guide bearing so that the shaft would not try to 'wobble' when you turn it quickly

It consists of a body, two thrust bearings, and oilite bushing, and some thready bits. I would love to take it to pieces to take some photos of the elements but I've just fitted it and I'm exhausted!

I also made a new shaft as the original wasn't long enough to accomodate my design.

Here's some pics:

The end result is absolutely brilliant, in fact it's too good, the handle turns so freely that it rotates by gravity if left at 3 oclock or 9 oclock, so I'm going to have to try to add more friction somehow!

Perhaps more importantly I can now tighten the gibs quite tightly but the bearings will not present increase friction to rotation of the handle, and, I can wind the compound slide all the way in without the screw binding because of the misaligned factory parts.

It also does away with the very awkward pair of 17mm nuts that you had to adjust on the factory setup. Instead I have a threaded nobbin thing that screws onto the end of the shaft into the handle until tight, then a set screw goes through the middle of that to tension it up. Because of the twin thrust bearings you can squeeze the whole assembly really tight without any increase in friction and eliminate all backlash from the mechanism.

Really happy with this. Just need to make a leadscrew handwheel, do a similar mod for the cross slide and finish my DRO's and I'll have everything more or less there!

Offline Bernd

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Re: Mini lathe compound handle bearings
« Reply #1 on: June 12, 2011, 07:38:38 PM »

I think you need a counter balanced handle now.  :smart:

You can't fix "STUPID".

Offline Henning

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Re: Mini lathe compound handle bearings
« Reply #2 on: June 14, 2011, 02:45:14 AM »
Nicely done  :headbang:
I was looking at doing something similar the other day, but my primary goal was to get more space to avoid interference between the compound and carriage handle.
May as well go the whole mile and add bearings etc.  :dremel:
ANOTHER project for the list...  :proj:

Just because i can't, doesn't mean i shouldn't?
Tool- lover, with a collection to show for it!

Offline loply

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Re: Mini lathe compound handle bearings
« Reply #3 on: June 14, 2011, 07:37:58 AM »
Had a bit of a play with this set up last night and I think one critical benefit is the ability to clamp down the gib strips and retain useable handle resistance.

In the old system if you made the gibs tight the two parts of the handle were pushed tightly against each other causing massive friction, which on top of the tight gibs meant the handle was barely moveable.

With two thrust bearings this doesn't happen and I've been able to make the gibs much tighter than previously possible, which can only be good for rigidity and accuracy.

Couldn't recommend it highly enough therefore, if you want a nicer user experience and a more rigid compound, this is the way.