Myford 254 thread dial indicator

[Philip SlaterParticipant @philipslater86297]

Hi

Would anybody be able to tell me where I can obtain a thread dial indicator for the the Myford 254 please.

[Philip SlaterParticipant @philipslater86297]

[Philip SlaterParticipant @philipslater86297]

Hello again I'm guessing from the lack of response that thread dial indicators are not available anymore. Certainly all the Google searches that I've done don't show anything, plenty of Myford super 7 TDIs but nothing for the the 254.

Is it feasible to cut threads by closing the leadscrew half nuts and using forward and reverse motor directions for each cut. Obviously not disengaging the half nuts until the threads complete. I've got a DC brake fitted to the lathe which stops the chuck instantaneously.

[Neil WyattModerator @neilwyatt]

Posted by Philip Slater on 09/09/2019 09:47:34:

Is it feasible to cut threads by closing the leadscrew half nuts and using forward and reverse motor directions for each cut. Obviously not disengaging the half nuts until the threads complete. I've got a DC brake fitted to the lathe which stops the chuck instantaneously.

That's the usual way; reversible lathes are often supplied without thread cutting indicators.

Neil

[Philip SlaterParticipant @philipslater86297]

Thanks for that. Maybe not so good on the motor and all the switch gear but looks like the only way out.

Phil

[not done it yetParticipant @notdoneityet]

Nearly everyone with a metric lathe needing to cut imperial threads do it that way. Same for those with imperial lathes who wish to cut metric threads…

[Clive HartlandParticipant @clivehartland94829]

I have the sales brochure and available parts for the 254. the part. no. 95/136 for metric threads, in the listings priced at £100.81.

Note. it is only for use with metric threads. it goes on to say that if used with the imperial conversion set. 95/078 on a 254 lathe the leadscrew nut must remain engaged.the part no. for the imperial thread ind. iis 95/105 and cost £36.89.

Hope this is some help Clive

[speelwerkParticipant @speelwerk]

Is it not possible that the imperial TDI is the same as used on the 7 series? Niko.

[Philip SlaterParticipant @philipslater86297]

Thanks Clive I'm assuming the sales brochure you have is from when the lathe was in production or are you suggesting that the parts are still available, in which case I'm all excited. My lathe is metric I had a similar thought that the 7 series TDI might be compatible but it's a 3mm pitch leadscrew.

[lfoggyParticipant @lfoggy]

I have a metric 254 with the 3mm pitch leadscrew and it has an indicator fitted for cutting metric threads. It is a simple device and it would be possible to make one. It is basically a metal body which holds a gear against the leadscrew. There are two gears to choose from (28 and 30 tooth) depending on what pitch you are cutting. There is a dial with divisions connected to the gears that then indicates when to re-engage the half nuts. The metal body would be basic machining and you would need to be able to cut the gears You would need to find an original to copy, particularly for the divisions on the dial.

If you are anywhere near Birmingham you are welcome to inspect and measure up mine….

[Philip SlaterParticipant @philipslater86297]

Thanks for the offer Ifoggy I'm up in North Lincolnshire so a bit far to travel. I've never machined gears but I've got a milling machine so have the tools. Thinking aloud I wonder if I could machine the gears from Tufnel. Not sure what you mean by having 2 gears, are you saying you need to change gears on the Thread dial indicator?

[DC31kParticipant @dc31k]

Posted by Philip Slater on 09/09/2019 19:09:58:

I've never machined gears but I've got a milling machine so have the tools. Thinking aloud I wonder if I could machine the gears from Tufnel. Not sure what you mean by having 2 gears, are you saying you need to change gears on the Thread dial indicator?

Do not be alarmed: a thread dial indicator is in no way a precision mechanical device. Almost any kind of tooth shape will work; the important thing being the number of teeth (even so far as straight gashes around the perimeter of a thin gear.

You would do very well to buy Martin Cleeve's book on screwcutting as it probably the most concentrated source of information on leadscrew indicators out there. You can also search this site (using Google with site:model-engineer.co.uk as part of the query string – since the forum search is totally useless) as the subject has been done to death here as well.

Very briefly, thread dial indicators for an imperial leadscrew are very simple because of the way imperial threads are defined (teeth per inch) and one gear will do all pitches.

TDI for metric leadscrews are more complicated because metric threads are defined by pitch. One gear will not do all pitches. However, in some ways metric pitches are simpler because any pitch that is a factor of the leadscrew pitch does not need an indicator at all – you can drop the nuts in anywhere they will engage.

For your 3mm pitch leadscrew, this means 3.0, 1.5, 1.0, 0.75, 0.6, 0.5, 0.3, 0.25 and 0.2 pitch threads do not need a gear. The remaining common ones (especially 1.25 and 1.75) will need an indicator gear (1.25 needs a gear with teeth 'by fives' and 1.75 needs a gear with teeth 'by sevens&#39.

[Philip SlaterParticipant @philipslater86297]

Very interesting. As your probably realising I still consider myself a novice when it come to machining. Looks like I need to be getting that book you mention. Thanks for the input.

[Clive HartlandParticipant @clivehartland94829]

Hi Phil, the brochures are 1999 vintage so not current and as you say the lathe is out of production.

I had just purchased an ML10 so wanted the brochures to get bits I wanted.

Clive

[ianjParticipant @ians]

Phil.

May be worth emailing David of "Quillstar" as he says on his web site

A few 254 bits including lathe beds, aprons, tailstocks, screws, nuts, dials etc. "

http://www.quillstar.co.uk/

Quillstar

[not done it yetParticipant @notdoneityet]

Using a plastic gear against the lead screw would reduce any risk of wearing the lead screw. A spur gear will wear in OK as there is no real load on it.

[lfoggyParticipant @lfoggy]

There are two gears on the indicator and you choose the one appropriate for the pitch you are cutting. The gear is selected by undoing a nut, removing and replacing the gear. As stated above, as long as the tooth count is correct it wont matter too much if the tooth profile on the gears is not perfect. If you are planning to do a lot of thread cutting I think making an indicator is definitely a realistic prospect.

[Thor 🇳🇴Participant @thor]

Posted by Philip Slater on 09/09/2019 19:09:58:

Thanks for the offer Ifoggy I'm up in North Lincolnshire so a bit far to travel. I've never machined gears but I've got a milling machine so have the tools. Thinking aloud I wonder if I could machine the gears from Tufnel. Not sure what you mean by having 2 gears, are you saying you need to change gears on the Thread dial indicator?

I used Delrin to make a 28T gear wheel for my metric lathe (3mm pitch leadscrew), it has worked well for many years so Tufnol (sheet) should work well. A 30T gear was supplied with my Thread Dial Indicator.

Thor

Edited By Thor on 10/09/2019 05:15:01

[ianjParticipant @ians]

Phil. I've just spotted this one on ebay:

0sAAOSwXrld1ua~”>Myford 254 thread indicate

[IanHParticipant @ianh]

Hi,

I have an imperial 254 in Cheshire if you want a look.

Ian

[Derek GreenhalghParticipant @derekgreenhalgh23299]

Some very helpfull information in this thread for all I don't have the said lathe, mine is an HBM 250g with a metric 3mm lead screw that came without a thread dial. It also came with a gear to change to imperial threading.

Reading the thread it seams i can make a thread dial, disengaged for most metric threads but with a 20 and 21 tooth gear engaged I'm covered for 1.25 and 1.75 metric pitches that are very common

what gear cutter would i need to cut a gear compatible with a 3mm pitch lead screw? if I'm on the right track its like a 3mm rack as in rack and pinion. In effect i have the 3mm rack(lead screw) so all i need to do is make the pinion and skew it a couple of degrees to get it to mesh better

I have never made a gear before but have a mill, rotary table with chuck and tailstock, The gear cutters for metric are identified M0.5 M1 M2 etc in sets of 8, how do you work out which set I need to match the 3mm pitch? It would be nice to have them all but they are not cheap.

thanks

Derek

[not done it yetParticipant @notdoneityet]

Hi Derek,

I suggest you read the helpful information, regarding those gears, already in this thread.

Here is just one of them “even so far as straight gashes around the perimeter of a thin gear.”

[DC31kParticipant @dc31k]

Derek,

The term you are seeking is 'circular pitch'. The leadscrew has a pitch of 3mm. Acting as a rack, it has a pitch of 3mm. The proper gear to mesh with it has a pitch of 3mm, albeit that pitch is wrapped around a circle, hence circular pitch.

In metric gear terminolgy, a 1MOD gear has a circular pitch of pi (3.14mm). For 3mm circular pitch, you would need a cutter of 0.95MOD which is very non-standard. Hence, I would use an M1 cutter.

There is another issue to mention, but about which you need not concern yourself for a TDI gear, and that is pressure angle, the gear equivalent of the thread angle of your leadscrew. Your leadscrew, if metric, will have a trapezoidal thread of 30 degree angle. The correct gear cutter should have a pressure angle of 15 degrees. Standard metric cutters are 20 degrees, but it does not matter in this case.

Each cutter in the set of 8 has a range of teeth which it is good to cut. So you pick the cutter to suit the number of teeth in the gear you are cutting. I hesitate to mention a number for you as a lot of modern Chinese-sourced cutters have the numbers reversed to the traditional system (1 in traditional is 8 in Chinese).

When cutting the gears, I would be tempted to cut them both on the same size blank (i.e. a blank sized for twenty and a half teeth) then you do not need to alter centre distance when swapping gears. Also cut them relatively thin and you do not need to worry about skew angle.

If there is enough space for it to fit, consider cutting a single 35t gear and having interchangeable graduations on the dial (sheet metal held on with magnet, 5 graduations one side, 7 on the other). It is a lot easier to flip this over than to fiddle about behind the apron changing gears. The biggest challenge with this is finding the space for a relatively big gear.

[Keith LongParticipant @keithlong89920]

Hi Derek, as DC31K points out the gear that your after is pretty close to 1MOD, so the easiest, possibly quickest and by far the cheapest way to find out if a 1MOD gear will do is to buy a moulded plastic 1MOD gear with the number of teeth you need and try it. Plenty of suppliers around a quick search of the internet will throw up plenty, and you only need a cheap and cheerful one, no need to spend out for a fully machined precision one at this stage. That way you can get the design of your TDI sorted and if you feel like it change to a metal gear later.

Edited By Keith Long on 13/04/2020 16:10:04

[Derek GreenhalghParticipant @derekgreenhalgh23299]

Thanks for both replies, where the TDI fits on the rear side of the carraige there is quite a bit of room, its fitted with only 1 bolt and is swung into mesh when needed

​​​ Some photos here (if it works)

I take it a 35 tooth gear will cover 1.25 and 1.75 in one instead of making a 21 and 20, I'll have to make the body too so that might be the best way to go. I have a 3d printer so i might try to find an .stl for that gear on thingiverse as my cad drawing sucks, and have a play about and se what fits the best then buy the cutter and make a better one or a roll of carbon filled abs or PetG filament. It will give me something to do in this confinement. Today here in Spain some people have been alowed back to work so the posral system should be up and running again if i need something.

thanks again

cheers

Derek

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