Harrison M300

[northwest]

As many of you know I have a Harrison M300 and it has everything you could want, it is fast, accurate and very little backlash. BUT it has one annoying "feature", the cross slide screw is worn in the middle, it is really, really annoying and I cannot take out the wear with the anti-backlash wedge because if I do I cannot turn the bloody handle at the extremes. So, my question is, does anyone know of a source of 16 x 2.5 mm ACME threaded rod or know where I can get a new Left hand metric screw for this? I have considered converting it to ballscrew but this has no resistance and would wind on with the size of some of the cuts I take. All suggestions gratefully received.

 

[Milkybars]

https://millhillsupplies.co.uk/ *may* be able to supply one

 

[Seadog]

As many of you know I have a Harrison M300 and it has everything you could want, it is fast, accurate and very little backlash. BUT it has one annoying "feature", the cross slide screw is worn in the middle, it is really, really annoying and I cannot take out the wear with the anti-backlash wedge because if I do I cannot turn the bloody handle at the extremes. So, my question is, does anyone know of a source of 16 x 2.5 mm ACME threaded rod or know where I can get a new Left hand metric screw for this? I have considered converting it to ballscrew but this has no resistance and would wind on with the size of some of the cuts I take. All suggestions gratefully received.

You'll almost certainly need a new, too.

 

[Agroshield]

...does anyone know of a source of 16 x 2.5 mm...

2.5mm pitch is very non-standard for any trapezoidal thread. Standard pitch for 16mm dia. is 4mm. You can only generally get smaller pitches in smaller diameters.

Go to any one of these and try to find anything with that pitch:

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There are people who would make one for you, but it likely would not have leadscrew accuracy: https://www.autolinearmotion.com/t12-lead-15mm-pitch-2-5mm-tr12x15-trapezoidal-lead-screw.html

I would be looking at the higher end Taiwanese and Chinese lathe manufacturers to see if they had a cross slide screw and nut available as a spare part. Grizzley in the US might be a good starting place to find the part and then find a seller of the same machine in a different colour. Do any of the import milling machines use 2.5mm pitch leadscrews?

Posithread in the UK sell 2.5mm TR inserts (check that they do a LH version) if you wanted to make your own screw. You could probably just make the screwed portion and sellotape the existing dial and cross feed drive end onto it.

Another way is not to worry about the pitch and make a new dial to suit the pitch of the new one (does anyone make a rotary indexer for the desktop lasers?).

 

[dave h 2]

As many of you know I have a Harrison M300 and it has everything you could want, it is fast, accurate and very little backlash. BUT it has one annoying "feature", the cross slide screw is worn in the middle, it is really, really annoying and I cannot take out the wear with the anti-backlash wedge because if I do I cannot turn the bloody handle at the extremes. So, my question is, does anyone know of a source of 16 x 2.5 mm ACME threaded rod or know where I can get a new Left hand metric screw for this? I have considered converting it to ballscrew but this has no resistance and would wind on with the size of some of the cuts I take. All suggestions gratefully received.

Imperial lathe?
Acme is Imp and most 5/8 Acme leadscrew is 8tpi
Trapezoidal is metric and most 16mm leadscrew is 4mm pitch
2.5mm is a little fine

Bit of an overlap with Agroshield, but are you mixing your measurements

 

[Agroshield]

How does the backlash adjustment on the nut work? You call it a 'wedge' above, which suggests something solid. Is there any way to convert the mechanism into a spring action (rubber wedge?)? Then it will self-adjust as you go from the unworn to worn part of the screw.

Lots of anti-backlash gears work in that way: the gear is split in half down its width and each half is spring loaded against its mate.

See also for principle: https://ooznest.co.uk/product/acme-anti-backlash-nut/

 

[Agroshield]

...are you mixing your measurements

It was likely Harrison mixing their measurements. There was discussion of a similar issue on the Model Engineer board.

In summary, when the UK lathe manufacturers wanted to build a metric model, all they did was cut a metric pitch on their existing leadscrew blanks.

So his cross slide screw is highly likely to be 5/8" x 2.5mm pitch ACME form. Of course it is non-standard, but it makes manufacturing so much easier. All you do is flip a lever on your leadscrew threading machine from 10 tpi to 2.5mm and keep going. No keeping two sizes of blank in stock; no keeping two sets of cutting tools in stock.

I wonder about the modern Chinese machine manufacturers when they now produce for the US market. Do they do similar? Will your Grizzley lathe have a 25mm dia. x 8tpi trapezoidal form leadscrew?

 

[Seadog]

If you've got a DRO a cross slide screw doesn't need to be quite so accurate.

My Rong Fu used a 23 x 2.5mm feed screw for the X axis.
I have some inserts that I managed to find after much searching, if you want to try to make your own.
I converted (am converting, WIP) to ballscrew.

 

[Agroshield]

My Rong Fu used a 23 x 2.5mm feed screw for the X axis.

You just have to check the handedness. The lathe cross slide has to be left hand. On a mill, I think it is usually the Y that is left hand.

 

[Seadog]

You just have to check the handedness. The lathe cross slide has to be left hand. On a mill, I think it is usually the Y that is left hand.

My mill is RH on the X and LH on the Y.

 

[addjunkie]

Have you enquired about the new spare price from the 600 group

 

[northwest]

If you've got a DRO a cross slide screw doesn't need to be quite so accurate.

Quite correct but it is a bloody nuisance when the handheel slips half a mil because you have come off the tight part onto the "free" part of the leadscrew. It is just a bloody nuisance and can create a good deal of scrap.

 

[northwest]

Have you enquired about the new spare price from the 600 group

I shall call them in the morning but I am sure I know the answer before I start and it will be eye watering.

 

[Pete.]

You just have to check the handedness. The lathe cross slide has to be left hand. On a mill, I think it is usually the Y that is left hand.

No need to check the actual screw the rule is simple:

If the handle moves with the slide, it's a RH thread. If the handle does not move with the slide the thread is LH.

There are some exceptions but very very few.

 

[minimutly]

No need to check the actual screw the rule is simple:

If the handle moves with the slide, it's a RH thread. If the handle does not move with the slide the thread is LH.

There are some exceptions but very very few.

Hmmm. Do you mean handle clockwise slide in - RH and vice versa?
Edit, engage brain Huw - clockwise turning handle, RH thread will bring the the table out towards the handle - won't it.

 

[Pete.]

Hmmm. Do you mean handle clockwise slide in - RH and vice versa?
Edit, engage brain Huw - clockwise turning handle, RH thread will bring the the table out towards the handle - won't it.

No I'm specifically talking about lathe slides since the query is for a cross slide screw.

EDIT: I missed that the conversation had drifted to include mill slides.

 

[Agroshield]

Hmmm.

When he is talking about the handle moving, he is meaning any non-rotational (i.e. lateral, translational, left-right, in-out) movement thereof.

Think of the difference between the cross slides of a Myford and (for example) a Bantam.

On a Myford, the screw is fixed to the cross slide and the nut is attached to the saddle. The RH screw moves in and out when you rotate it. On a Bantam, the nut is fixed to the cross slide and the screw is fixed to the saddle/apron. The LH screw does not move in and out when you rotate it.

Seadog suggested the X-axis screw off a Rong Fu-type mill as a candidate to replace the M300 cross slide screw (because it has the required 2.5mm pitch), but it would not work as it would be the wrong (Rong?) hand.

 

[Seadog]

When he is talking about the handle moving, he is meaning any non-rotational (i.e. lateral, translational, left-right, in-out) movement thereof.

Think of the difference between the cross slides of a Myford and (for example) a Bantam.

On a Myford, the screw is fixed to the cross slide and the nut is attached to the saddle. The RH screw moves in and out when you rotate it. On a Bantam, the nut is fixed to the cross slide and the screw is fixed to the saddle/apron. The LH screw does not move in and out when you rotate it.

Seadog suggested the X-axis screw off a Rong Fu-type mill as a candidate to replace the M300 cross slide screw (because it has the required 2.5mm pitch), but it would not work as it would be the wrong (Rong?) hand.

It wasn't a suggestion, just the mention of another machine with a non-standard 2.5mm pitch thread.