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[garryhParticipant @garryh]

<li style=”text-align: left;”>Hi all

I just joined the forum as I am about to embark on some kind of project to satisfy my constant need to create. Not sure where to start.

I come from an engineering background having been a turner back in the eighties. I also programmed cnc lathes although not much use here.

Garry

[David George 1Participant @davidgeorge1]

Hi Garry welcom to the forum. What tooling do you have as I only got started with making bits after I aquired a lathe Which started me making a model lathe from Stuarts which then got me into making tooling to allow me to make that and other bits. I made a wobbler simple steam engine, then had to make a boiler to power it and on and on. I ended buying a small mill as milling on a lathe has limitations and that further makes other ideas possible and have made spares for other machinery and repairs.

David

 

[Harry WilkesParticipant @harrywilkes58467]

Welcome to the forum Garry

H

 

[noel shelleyParticipant @noelshelley55608]

Welcome to the forum Garry. This engineering lark effected me at about age 7, and it just got worse ! But it is very interesting. Where abouts are you ? Best wishes, Noel.

[garryhParticipant @garryh]

Hi David.

I currently only have a faircut Junior Lathe that I bought cheaply. It came with missing backgears and just a 3 jaw chuck. I am currently sourcing bits and pieces to get myself a usefull machine. The chuck backplates are unavailable for thes as the spindle nose is 3/4 12 UN.

 

The backgears are causing some confusion as lathes.co.uk states that they are the same as a drummond at 14dp. However after taking some measurements they appear to be 16dp 14.5° pa?

 

I do have a good selection of drillbits, reamers and taps dies that I kept after selling my Boxford AUD after closing down my workshop.

 

I currently live in a small flat so have limited space available and have changed the counter drive system and motor. Photo’s below.
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It is a case of trying to source bits and pieces before I can get going.

 

Garryh

[garryhParticipant @garryh]

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[garryhParticipant @garryh]

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[garryhParticipant @garryh]

Thanks for the welcome Harry and Noel. I am in Ashton Under Lyne Manchester

Garryh

[Howard LewisParticipant @howardlewis46836]

Welcome!

You are sure to find help on here.

Are you sure that the thread is 3/4 x 12 Unified?

12 tpi is not a standard for UNF or UNC.

But 3/4 BSF is 12 tpi.

Catch 22, without changewheels, you can’t screwcut a backplate!

If you have  a 3/4 BSF tap, you should be able to find a backplate (See what Arc Euro can offer. I modified one, by bushing and retapping, for a friend to take a 4 jaw chuck for his old small lathe )

They also have 80, 100 and 125 mm chucks on offer, and a range of backplates which you could modify to fit your lathe.

Changewheels may be hard to find.

Check tooth count against OD to find the DP.

Hopefully you could then find ones that can be bored or bushed to fit your lathe.

You are experienced, so these activities should present little problem for you.

Good Luck

Howard

[garryhParticipant @garryh]

Hi Howard. Thanks for the welcome.

You are probably right regarding the spindle nose, although I checked it with an American pitch gauge and it looked right for the 60 inclusive. I will get the magnifier glass out as my eyes are not what they used to be.

I do have an homemade tap of M19x2 (0.1 pitch error) that I made for making attachments to fit the Dremmel. One of those attachments fitted the spindle perfectly. Cuts a really nice thread in ally but never tried it on steel or cast iron.

I can’t imagine faircut adopting american standards back then either.

It may be wise to get a full set of ML7 change gears and adapt those as they seem to be pretty easy to get a hold of.

Garryh

 

 

 

[BazyleParticipant @bazyle]

See if you can find someone to 3D print gears for you, perfectly adequate on a small lathe.

Double check the DP of the changewheels. I have just looked at the pages on Lathes.co.uk and the pictures show gears with a pin and hole to connect them not a keyway, ie like Drummond. This might be because some owner of the example changed to Drummond gears as easily available. However there is a catch. The RandA series of lathes and clones used a pin too but very different – the pin is only about 3mm, parallel not tapered and those wheels are 20DP like Myford. Lots of RandA lathes come with modified Myford wheels.

[garryhParticipant @garryh]

I used the calculation that I found on this site

For the 20 tooth gear= 1.3779″ OD

=Number of teeth + 2/dia

=22/1.3779=15.966 so got to be 16dp

These gears have a drive pin too.

They are 5/8 wide, 5/8 bore and 1/8 pins on 0.900 crs

 

I have been looking at getting a 3d printer so might be a good enough reason. I told myself that I would learn to use onshape software before I delved in. I am already used to using 2d software.

Garryh

[Howard LewisParticipant @howardlewis46836]

Looks like the changewheels are 16 DP. Myford are 20 DP, so unless you plan to change the whole set up, (Can you change the gear at the back of the spindle?) you may be stuck with a compound of some sort to mesh them together.

Unless you can find suitable 16DP gears, the lathe is going end up as a bit of a hybrid; although if it does what you want, will that matter? Try posting a “Want” with the gear spec

Using Myford gears would be easiest since they are fairly freely available, and they are 14.5 PA.. 7 Series are compounded with a key, where those for ML1, 2,3 and 4 use a 3/32″ pin, and 5/8″ bore.

The Myford gears would only need drilling part way through for the 1/8″ driving pin.

Or, you don’t mind plastic gears (Although metal sets are available) you could use Module 1 gears from a C2 or C3, but the problem might be changing the first driver to a 20T Mod 1.

Plastic gears for Chinese mini lathes use 3 or 4 mm keys, depending which factory made the machine.

Metal gears from Arc Euro Trade will have 3 mm keyways, since they are intended for machines made by Sieg

If this is possible, all will certainly need modification, (boring out or bushing) and then making up a new studs for the intermediate gears, so that the final driven gear will fit onto the Leadscrew.

HTH

Howard

[garryhParticipant @garryh]

The spindle gear is changable. It has 20 teeth as does the leadscrew gear. There is also a 45 tooth already on the banjo. I would have to source the rest. Knowing which to get is the problem. I suppose I could start off with a couple to get some common pitches. They are generall £20+ per gear secondhand so could get expensive.

Garryh

[garryhParticipant @garryh]

<p style=”text-align: left;”>I decided to keep the change gears to original spec of 16dp. I sourced some second hand from Ebay. 40,60,70,70t and should arrive this week. With what I have already there are</p>
20,20,40,45,60,70,80. I need to find a 127t to give me the Metric threads that I will use so i will put a wanted ad on the site.

Garryh

[BazyleParticipant @bazyle]

You can make a good approximation to metric with a 63 or a combination using 46&73. There are lots of tables of changewheels online. You will need some ending with 5 like 25, 35, 55, 65 all of which can be 3D printed.

[garryhParticipant @garryh]

Something is puzzling me, Why does this math work:

Assuming I have a 20t on either the spindle or leadscrew and a 55t on the other with an 8tpi leadscrew, then 20×55/50=22tpi

[garryh]

On garryh Said:

Something is puzzling me, Why does this math work:

Assuming I have a 20t on either the spindle or leadscrew and a 55t on the other with an 8tpi leadscrew, then 20×55/50=22tpi

I’m too fuzzy headed to attempt that, and the numbers I offer next could be wrong too!  Check them yourself.

Manually calculating the gears needed to generate threads on a lathe is labour intensive.  Continued fractions if anyone wants to look it up.  Same method used to find fractional approximations of pi, 3, 22/7, 333/106, 355/113, 103993/33102, 104348/33215, etc.  Don’t bother with fractions myself – 3.142 is easier.

An alternative is to program a computer to generate all the permutations available from a given set of gears.   Though the maths is much simpler, it’s rarely done by humans because the number of permutations is enormous, doing the sums takes forever and the work is extremely tedious.   Though it can take a long time to print the results, a computer whizzes through the same problem in microseconds:  doesn’t get bored, and does sums in giga-floating point operations per second.   Ages ago I wrote the necessary program, partly to find out what unadvertised threads are possible on my WM280.   Loads of them, mostly useless!

I fed garrys list of gears into the program [ 20,20,40,45,60,70,80 ] and told it he has a 1/8 leadscrew.  Short list of useful TPI follows:

List is filtered because, for example, there are 16 different combinations of garry’s gears that all produce 8TPI.  I just printed the first.

Garryh’s gears aren’t metric friendly, though there are a few near misses, for instance 5 ways of producing close to a 1.0 pitch.  1.021 is 24.89 turns per banana which garryh can do with 6 different gear combinations:

Teeth………. Ratio. Metric. .. TPI
60 80 45 70 9/224 1.0205 24.89
40 80 45 70 9/224 1.0205 24.89
40 70 45 80 9/224 1.0205 24.89
20 70 45 80 9/224 1.0205 24.89
60 70 45 80 9/224 1.0205 24.89
20 80 45 70 9/224 1.0205 24.89

As to which gears to buy without doing sums, many imperial lathes have 1/8 ratio lead-screws, so it’s a good bet that gears supplied with them will deliver useful ratios on garryh’s lathe.  A potential minor gotcha is modern lathes may not deliver the required ratios in obvious ways.

• A 127 toothed gear works straightforwardly by converting inches into millimetres.  Direct and accurate but requires a large diameter gear that may not fit on the banjo.  Check whether or not a big gear will fit on your lathe before buying one!
• 63 toothed gears are a practical size, but the accuracy of the metric conversion drops.  63 tooth approximations may not be as inaccurate as might be expected, because the maths is different – not a direct conversion as with 127 teeth.
• The “different maths” approach to ratios is often taken by modern lathes.  They come with gears allowing close approximations of both metric and imperial threads, not necessarily obvious!   The advantage is fewer gears are needed.

Quite interesting to compare metric and imperial versions of the same modern lathe.  A metric WM280 comes with 11 gears (5472 permutations), whilst the Imperial version has 13 (12540 combinations).   Oddly, it appears that a metric WM280 can do a few more of the less useful TPI threads than it’s Imperial sibling.  However, not checked, I expect some of the metric lathe’s TPI approximations are mildly inferior to the imperial lathe, whilst the Imperial machine does a few metric pitches a tad inaccurately compared with its metric sister. For the difference to matter, the operator has to be doing something special, like cutting a very long high accuracy thread, for which a general purpose lathe isn’t the right tool anyway.

Dave

 

[BazyleParticipant @bazyle]

Imperial changewheel sets normally include a 38 used for 19tpi 3/8 BSP. You might not need to rush to get that one.

[Russell EberhardtParticipant @russelleberhardt48058]

Before rushing out to buy a 127 tooth wheel, have a look at the program NThreadP available as a free download from Lathes.co.uk.  You can load all the gears you have and ask it to calculate the combinations that will get you close to any metric thread you need. It also tells you the pitch error for any given combination.

Yes, 3D printed gears work fine.  As an experiment, some years ago, I printed a 16/32 double gear for use in the fine feed train for my Atlas lathe to see if it would reduce the noise and it has been there ever since.

Russell

[Howard LewisParticipant @howardlewis46836]

55/20 = 2.75. This setup, (The 50 is purely an idler, to fill the gap and ensure correct direction of rotation) will cause the Leadscrew to rotate 2.75 slower than the Spindle, so that there are more turns of the work for a given travel of the cutting tool..

With a 8 tpi Leadscrew, this will give 22 tpi

With a 8 tpi Leadscrew,the set ups recommended for any lathe with such a pitch will provide what you want

If you want to have hard copy, buy No 3 in the Workshop Practice Series, “Screwcutting in the Lathe” by Martin Cleeve, or the more expensive “Gearing of Lathes for Screwcutting” by Brian Wood.

Although I suspect that the W P S book may be the better for you purposes.

T produce a given pitch from a 8 tpi lead-screw, you need to work out the ratio between the desired pitch and the 8 tpi, and then set up a train to give that ratio.

Some easy examples:

For 12 tpi you would need a ratio of 1.5:1, such as 40:IDLER:60. For 10 tpi, (1.25:1) you could set 40:IDLER:50, for 16 tpi (2:1) set 20:IDLER:40

The book gives examples for many thread pitches

If you have to set a compound train, you will need to use the Tumbler Reverse, unless you want to cut a Left hand thread.

If you want to set up for a fine feed, a simple geartrain such as 20:70/20:80 will give 0.0089″/rev, which is still a little coarse, to my mind.

With a 30T gear as well, you could set up a compound train, 20:70/30:60/20:80 which would halve the feed rate to .00046″/rev. which would be better, but you need to use the tumbler reverse to have the feed towards the chuck.

If you can get the 5T intermediate gears, replacing the 70 by a 75, and the 60 by a 65, you will be able to obtain an even finer feed.

HTH

Howard

 

[garryhParticipant @garryh]

Thanks for all the input. A lot to take in.

I am going to get a small rotary table and laser print some custom scales in acrylic to try some smaller gears as I have a set of 0.5 mod cutters that I hope to use to built a rotary planetarium simulator model that caught my eye.

Unfortunately I sold My Elliot Mini Jig borer and dividing head when I closed down my workshop.

Garry

[Howard LewisParticipant @howardlewis46836]

A 127T gear, if there is room to fit it in, will allow metric threads to be cut more precisely than using a 63T.

Although for smaller sizes, no doubt, you will have the taps and dies needed.

For your Rotary table,try to get one with as high a ratio as possible, and a set of division plates will make life easier, if available.

Good luck!

Howard

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