Threading feed table & calculators, do not match.

This is the 60 tooth fitted in the uppermost position, i had to grind the nut to move it this high on the bar.

Swinging the arm over, and it only just makes it, It will almost swing under the spindle gear but not quite.

I tried the 1.75 thread and it came out way off. I cannot remember what it actually cut. I tried several calculators and they were off. But i did suss it out, it seems a failed hard drive and old age has crept up on me and i have forgotten what worked.

Thanks for putting up with me.

You could grind a bit of one end of the nut that takes the 60T to improve the mesh if needed.

Looking at the chart I posted earlier with the idlers marked they have been rather naughty. Making a longer arm might help but you would need to check the gear pcd's to see if they mesh. The usual arrangement for a banjo is 2 slots in a V so for simple trains like pitches of 1 and 2mm a large gear would be placed up against the gear on the lead screw and then the whole banjo swung to engage the large gear with the spindle gear as well. The other slot being used for compound trains.

I wonder if looking at 0.6mm pitch if they have simply forgotten that the 50 wont mesh. In that case a longer arm might solve the problem - assuming that the rest do mesh. You would need to calculate the pcd's and check.

Frankly if I bought a lathe like that I would take it back.

John

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I did grind the nut slighty to round it off otherwise the 60 would not have meshed either. The teeth would have grated but not meshed properly.

The bar length does seem to be the limiting factor. If i extend it slightly and maybe add a 2nd slot for a main drive gear it wont affect the gear ratio will it? Just had a thought it may not change the ratio but it will change the direction. Perfect pitch threads but all left hand

You could be right.

Your best option is probably to calculate the pcd's of the gears in each train and see if things mesh on a longer banjo.

The ones with the V style banjo usually have extra gears running off the spindle gear to select either left hand or right hand threads. Things like ML10's if I remember correctly have a separate location for a certain size of idler for cutting left hand threads. It's positioned so that the banjo can mesh with it rather than the spindle. If it has the same number of teeth as the spindle all it will do to any train is reverse rotation.

John

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I would have expected a tumbler reverse and an idler before the screwcutting train on most lathes. Is anything missing?

Nothing missing Neil mine has no tumbler reverse just a banjo down to the gearbox

Fairly standard on all the 210, 250, 280, 290 type lathes.

Edited By JasonB on 09/07/2016 18:16:31

Might be useful to fit one then! It would solve the problem of adding an idler reversing the leadscrew.

Neil

As Jason said, nothing missing. No reverse option on the 2109, although i have seen a website, Steve? who fitted an extra arm with a gear to add reverse. He modified the gearbox cover also.

A longer Banjo is really needed.

I tried the 66/20 gear setup for my 8 TPI giving me 3.3 instead of 3.175, close enough, but that only left space on the banjo for a 60T gear. that had to move down very slighty and only meshed by the tip of the teeth. I didnt have room for a spacer to secure the gear also. I ran it on its slowest speed but the rattle from the gear didnt sound nice.

I think threading an 8mm hole with 8TPI is beyond me. How do you make a rigid bar to thread aluminium at that size? I tried a valve stem bent over but its too flexible.

Thanks.

Yes i would second that quite alot of lathes have no such function for reverse, though it is a very common and quite simple adaptation to do so, one only needs to fit an intermediary gear between another banjo, and hey presto tumbler reverse. I haven't got one though, i use left hand taps/dies if the need arises, although it is something to think about no?

Michael W

Will order some 1/2" or 3/4" thick plates and have a go at making one. Will mild steel be sufficient?

My local place can take a week or so to cut small parts though.

I never seem to make standard parts, where do you get an 8TPI tap from thats 8mm diameter?

Do i just make it longer or is it worth adding a 2nd slot?

You could mill out the slot in the banjo a bit further, infact it would probably be OK with an open end. If you do make another then aluminium would be easier to cut but mild steel a bit cheaper. I would just go for a bit longer.

8tpi on an 8mm dia rod will only leave you about 2mm core diameter which will be very weak and just snap as you try to cut it, what is this part for?

Edited By JasonB on 10/07/2016 07:13:49

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Sorry, Michael ... That's not quite true.

... "hey presto tumbler reverse" Yes, but not "tumbler reverse"

Tumbler refers to the clever mechanism that provides reverse at the shift of a lever.

MichaelG.

I would have thought an 1/2" or so thick aluminium section or plate would be ok. Not sure about open ended - the nut might cause it to spring open a bit unless things are dead square.

Seriously though DO calculate the pcd's of the gears and make sure it's worth doing. This is a rather odd fault for a lathe to have. Maybe they ran out of parts and fitted one off another lathe or maybe they couldn't care two hoots about the whole area and what ever you do it wont cut all pitches.

8mm dia 8tpi ? I don't think so even with a tap. 8mm core 8tpi maybe with a ground up hss tool. You would need some 1/2 square hss but even that is pushing limits and there will be a lot of spring in the tool that will need to be run out.

John

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Edited By Ajohnw on 10/07/2016 09:41:32

Looking at the picture, it does appear they didn't mill the slot as long as it could be.

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< Ahem ...>

He did mention an 8mm hole

MichaelG.

Yes it does look like it could go a fair bit longer. Just leave the same thickness's as the edges.

Might be well spotted Neil.

John

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Well spotted if that's the case Michael. It should be just about achievable with care but if it's following some design I would wonder why it was so small and probably adjust things to make it bigger.

John

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Tpi query solved, its the 8tpi square or ACME thread for teh seat adjuster so tool would be 1/16" wide and 1/16" deep giving a 5mm core. Though from picture it looks more like 10mm OD

Answer to how you cut the internal thread is to make yourself a tap from Silver steel.

Edited By JasonB on 10/07/2016 10:41:53

Is that an opto coupler to sense rotation I see on the top photo? Just add CNC then you can cease worrying about change gears!

OH MY....... NO!!! not another project I have 1001 on the go already...

Bought the mill recently and a rake of bits for it and my pockets are empty. Missus has this strange obsession with shopping for food etc. Can't be doing that when i need toois

And yes, its for the lathes rev counter.  I had to change the voltage regulator and some caps because that stopped working.

Edited By Dave Smith the 16th on 11/07/2016 19:32:13