You don't say what diameter handwheel you have used, the larger the handwheel the less effort needed to move the carrage.

Your 15T pinion may be a bit small, 15 x 3.142 = 47mm of carrage movement per turn of the handwheel, compare that with my lathe that moves 30mm per rev with a 125mm dia handwheel.

J

Just one other thought have you still got the feedscrew engaged?

Edited By JasonB on 21/11/2015 07:32:56

The lathe has a dovetail bed. I don't think these are generally fitted with a feed rack but at a smaller size Taig get away with it. The pinion gear is usually within the bounds of the saddle guides as well. It wont help moving it outside that.

One problem with the Taig that from the photo's uses the same arrangement is that the rack teeth face upwards so swarf gets on it. As there isn't much clearance it jams.

I'd say your best bet is to set the saddle up the same way as the other slides should be set up with some decent oil on them. Push by hand feeling for slight resistance when the gibs are set. It's way too easy to over tighten if the lead screws are used. Then with a decent sized hand wheel look for gearing that provides around 1" saddle movement per turn, typical for smaller lathes. On the other hand if it's stiff and may well be less than that would be easier – say 1/2" per turn, still a lot quicker than the leadscrew. Your rack has around 1/8" pitch so needs gearing up.

Jason may have a point about the leadscrew – I don't see a lever to disengage it from the saddle ??????

John

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Wabeco use a separate housing for the shaft that carries the rack gear and that's with an apron that 19mm round the edges thinning to about 12mm in from the edges and in cast iron. The hand wheel is mounted the same way – separate housing that fastens to the apron. If you do it that way and leave a bit of clearance you could adjust the mesh by moving them around a bit. One turn of the feed wheel on that moves the saddle by 30mm. The hand wheel is only 80mms dia though so for hand feeding it pretty hopeless. I'm going to change it to 110mm, still not great but a lot better. I'd have to change the gears to alter the feed on this one so it makes more sense to rough out with a hand feed. That's often the best way of finishing odd little bits anyway.

You may have misunderstood what I meant about the position of the rack gear. It ideally needs to be within the width of the saddle, not overhung at one end.

Oil – since I found it better than any other I use slideway oil off ebay. Some people drown the lathe in it. I find a bit a month or so is fine. It seems to hang around longer than others. I have heard from several people who have switched to using this sort of oil and all find it better. Some did use motor oil or the right grade of hydraulic oil to get a pure mineral oil. If the gibs aren't set correctly on all of the slides though results will be mixed. Some like the top and compound rather loose. Up to them really.

I'd seriously look at turning the rack over if I were you. I did have a Taig / Peatol once and swarf getting on the upward facing teeth was a right pain. These use a fine rack and small gear so the feed rate is usable even with the tiny handle. It's another thing you could play with – how much one turn of it moves the saddle. Even 15 or 20mm would be a lot quicker than the lead screw. There will be more friction from a dovetail bed but Taig get away with it by setting the gibs on the saddle as I suggested.

Silly me saying the rack gear needs gearing up. In a rush. From taking other lathes apart I would try for something like 20 teeth, maybe more, not too small, there and gears to provide what ever is needed for the feed rate.

John

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Edited By John W1 on 21/11/2015 14:12:49

Edited By John W1 on 21/11/2015 14:19:57

Crazy thought , use small bike type chain as rack, ends fastened to left and right of saddle. running over sprockets each end of travel. sprocket hand wheel on saddle to move it , I said it was crazy but it might work.

Maurice

No need to run a chain over sprockets at each end, as if it is fixed at both ends of the bed and engages with a sprocket on the saddle, it will behave like a rack and pinion (That is basically how a chain ferry works.) Two idlers could be used to keep the chain horizontal and run it around a sprocket on the apron in an omega shape, or if the chain could be mounted high one end and low the other a single idler could be used, as in the Brooks tool and cutter grinder described in MEW 16.

Moving the handwheel (well the pinion) so it is contained within the width of the saddle is likely to excacerbate the problem (if the problem is being caused by saddle lifting forces). If the rack/pinion engagement was say 2m off to the right, the vertical distance of the rack to the bedways would be much less of a problem.

Ideally the force imparted on a slide or carriage by a leadscrew or rack pinion should be as close too, and in line with, the interface of the fixed and moving surfaces as it can possibly be.

IanP

One way to use a short shaft carried in one plate would be to use a pair of thrust bearings on the shaft with the plate between them. The shaft would need to fit the bearings properly and be backed up by thick washers. If room is tight, look at magneto bearings.

Cheers, Tim

John

I misread what you were saying. I thought you meant that the handwheel 'had' to be in the width of the saddle whereas what you were inferring was that it was an 'ideal' placement. Machine controls are positioned for operating ease traded off with many other factors.

Ian P