Pin 28 should be fully 'home' in it's collar, not hanging out. It's purpose is to secure the collar to the leadscrew.

If it's not too badly damaged, it's okay to straighten it out and replace it – loosen off the nut and handwheel at the R/H end of the leadscrew and the carriage lock first to release any tension.

Once the pin is back in, re-fit the handwheel loosely (i.e. with ample end-float), and lightly nip up the locknut just to check that the leadscrew turns freely and without binding or rubbing on anything.

If you can't achieve free rotation at this stage, something else is amiss and will need sorting out.

Once everything feels free-but-sloppy, turn your attention to adjusting the handwheel to give the minimum of freeplay/backlash/endfloat, but without binding or becoming stiff to turn – it will not be possible to eliminate all backlash because some clearance is necessary for the parts to turn without binding.

It can be a pain to achieve correct adjustment, but it's worth persevering, and if you must, err on the side of too much freeplay rather than not enough.

The 'screw thread' pattern might be a seperate issue – is the gear train set up to give the finest feed possible – (0.08mm, I think) – 30 tooth (Z 30) on the back of the spindle, driving a Z75 which should be compounded with a Z20, which then drives the Z100 on the leadscrew…

There are a few 'hobbymat'  and 'MD65' threads on the forum, the machines are great, but have some quirks, you can use the search box at the top of the page to see previous discussions..

Edited By DiogenesII on 06/03/2022 19:32:51

Hi Harry, no it should not be the way you describe. The tapered pin shouldn't be showing any more than my one shown below and it should be able to be seen no more than the same amount on the other side of the bush- No. 8 on the drawing.

There shouldn't be a steel plate that the pin can rub on anyway, as there should be an aluminium apron No.1 on page 48 as shown in the above photo that holds change gears.

Regards Nick.

That's a possibility: a replaced shear pin suggests a previous owner crashed the saddle, which might have bent the lead-screw.

Fingers crossed, neither is a big problem. You can make a new shear pin without the lead-screw attached – I suggest Brass because it snaps more easily than Steel if there's another accident.

If the lead-screw is removed, there's a good chance you can ease it straight by gentle hand bending using a table top as reference.

Dave

I'd be surprised if the leadscrew is bent, it's a chunky fine pitch 16mm dia thing and quite short.. ..tho' of course the human animal can always find new ways to break things..

If you need a new pin, probably best to buy a new mild steel one – it is there to retain the collar that acts against the thrust bearing, and has to resist the push & pull of the carriage when the saddle is being traversed.

Agree with Bazyle that it's a standard 1:50 'Metric Taper Pin 3x18mm', – 3×20 will fit but will probably need to be dressed back flush with the collar after fitting.. also his comment regarding getting the holes lined up in the right orientation before driving home..

It is described as 'grooved' in the manual because the original part is a drive-fit taper pin with an axially 'nicked' head that's meant to retain the collar on it's shaft as a more-or-less permanent assembly.

If it works loose you might end up having to use a chemical retainer to secure it.

Edited By DiogenesII on 07/03/2022 07:25:45

Edited By DiogenesII on 07/03/2022 07:27:41

Hi, as DiogenesII has said and you can just make the number out in my photo above, just click on it and then click on it again and it should zoom in a bit closer and my book also says 51102

Regards Nick.

Hi Harry, I guess the only problem you will have, is the length of work piece you wish to turn down will only be 4/5's of the capacity of the lathe.

Regards Nick.

Check wether the bearing washers have the same inside diameters. Thrust bearings in some sizes have a housing washer that fits on the outside diameter into the housing and is clear of the shaft, whist the other washer fits onto the shaft and clear of any housing. Putting them the wrong way round will cause fretting on the shaft or housing.

On my machine the two innermost screws (on the front of the saddle) retain the leadscrew nut in it's housing in the saddle. The ends locate in a pair of shallow detent holes in the outer body.

The two outermost ones secure the tubular leadscrew guards on either side.

It'd probably be worth investigating further before doing much more – the leadscrew nut must be checked to make sure that it is correctly aligned and located, the securing screws should be 'home' but not tightened to the point where they are causing pressure on the screw, and the saddle must be completely 'free' to slide up and down the bed when unlocked – I might be inclined to adjust the saddle clamp / release screws to be on the 'slack' side until you get to the bottom of whatever is 'binding'..