By continuing to use this site, you agree to our use of cookies. Find out more
Forum sponsored by:
Forum sponsored by Allendale Jan 24th

63-tooth change wheel for Portass PD5

All Topics | Latest Posts

Search for:  in Thread Title in  
Rowan Sylvester-Bradley04/07/2020 18:01:25
30 forum posts

Can anyone suggest the best way to get a 63-tooth change wheel for a Portass PD5 lathe? The dimensions seem to be slightly different from those for the Myford 7. Ideally I would like a steel gear, rather than aluminium or plastic.

Thanks - Rowan

Brian Oldford04/07/2020 18:08:28
avatar
674 forum posts
18 photos

Assuming it's an imperial gear, do you know the DP? Myford change-wheels are usually CI.

 

 

Edited By Brian Oldford on 04/07/2020 18:09:12

Rowan Sylvester-Bradley04/07/2020 18:16:22
30 forum posts

If I have measured/calculated this correctly DP is about 12 (a 65 tooth gear has an outer diameter of 106.8mm). What does CI mean for the Myford gear?.

Thanks - Rowan

Pete Rimmer04/07/2020 18:20:32
734 forum posts
50 photos

Your gears are 16DP.

Andrew Johnston04/07/2020 18:22:54
avatar
5556 forum posts
650 photos

Pete beat me to it!

CI = cast iron

Andrew

The formula is: outside diameter = (number of teeth + 2)/DP

JasonB04/07/2020 19:48:46
avatar
Moderator
18318 forum posts
2024 photos
1 articles

Just to be sure that is Outside diameter in inches = (Number of teeth + 2) / DP

Brian Oldford04/07/2020 20:04:34
avatar
674 forum posts
18 photos
Posted by Rowan Sylvester-Bradley on 04/07/2020 18:16:22:

If I have measured/calculated this correctly DP is about 12 (a 65 tooth gear has an outer diameter of 106.8mm). What does CI mean for the Myford gear?.

Thanks - Rowan

For comparison Myford change gears are 20DP. According to **LINK** there's only a 75% confidence of it being 12 DP. whereas it's 94% for Mod 1.5.
The other important criteria id the pressure angle. Generally older gears tend to be 14.5° whereas more modern gears are mostly 20 °.

 

 

Edited By Brian Oldford on 04/07/2020 20:08:49

DC31k04/07/2020 21:22:43
214 forum posts
Posted by Brian Oldford on 04/07/2020 20:04:34:
...whereas it's 94% for Mod 1.5.

Would you care to reconsider your suggestion of a metric gear specification in the light of the following, courtesy of lathes.co.uk:

"Portass lathes date from the very early 1920s and were first badged as being made in the west of Sheffield "?

For clarity, I have greater than 94% confidence that it is Sheffield, UK.

Hopper05/07/2020 08:11:12
avatar
4653 forum posts
101 photos

If you are wanting to use the 63T gear to cut metric threads on your imperial lathe, you can do it without using a special 63 gear. Martin Cleeve's inexpensive book "Screwcutting in the lathe" has charts in it to cut all metric threads by using the original standard set of change gears in a compound set up. IE 20 to 65 in steps of 5. Accuracy is within 1 in 8,000, ie more precise than the orginal leadscrew will ever be. I've used his method on my ancient Drummond of similar vintage to your Portass and it works well. Cleeve's charts suit any lathe with an 8tpi lead screw, which is most old Brit iron including yours I believe.

Edited By Hopper on 05/07/2020 08:14:36

Brian Oldford05/07/2020 09:14:19
avatar
674 forum posts
18 photos
Posted by DC31k on 04/07/2020 21:22:43:
Posted by Brian Oldford on 04/07/2020 20:04:34:
...whereas it's 94% for Mod 1.5.

Would you care to reconsider your suggestion of a metric gear specification in the light of the following, courtesy of lathes.co.uk:

"Portass lathes date from the very early 1920s and were first badged as being made in the west of Sheffield "?

For clarity, I have greater than 94% confidence that it is Sheffield, UK.

I know that a Portass lathe has imperial gears. I was simply reporting what that particular web site said.

Roderick Jenkins05/07/2020 09:46:42
avatar
1897 forum posts
489 photos

Further to Hopper's comment, here is a table of metric pitches for a standard set of gears with an 8tpi leadscrew that I calculated:

 

basic gear set metric apprx.jpg

Whether you can get a combination that will mesh on your particular lathe remains to be seen but might be worth a try if all else fails.

stay well,

Rod

Edited By Roderick Jenkins on 05/07/2020 09:49:24

Bazyle05/07/2020 10:33:51
avatar
5292 forum posts
201 photos

I think this is an area where this forum could have a page that lists all known lathes changewheels specs and gradually build up the data from people with the actual lathe. It would alos help identify mystery wheels.
Lathe: DP/Mod, Pressure angle, thickness, hole dia, key type. Any other parameters?

As an aside the only 16DP gears I know of are the back gear on a Boxford.

I recommend against steel for changewheels. Too tough to cut . No strength is required in a small lathe so aluminium and good plastic like Delrin or Tufnol are adequate. Brittle plastic like Perspex obviously not suitable.

not done it yet05/07/2020 11:13:44
4744 forum posts
16 photos
Posted by DC31k on 04/07/2020 21:22:43:
Posted by Brian Oldford on 04/07/2020 20:04:34:
...whereas it's 94% for Mod 1.5.

Would you care to reconsider your suggestion of a metric gear specification in the light of the following, courtesy of lathes.co.uk:

"Portass lathes date from the very early 1920s and were first badged as being made in the west of Sheffield "?

For clarity, I have greater than 94% confidence that it is Sheffield, UK.

If you find it necessary to use an internet calculator to find/check the DP of a gear, do find a decent one.

By simple calculation, the DP works out to 15.98 - very close to 100% confidence that it is 16DP. From my simple calculation that should be clear there is no chance of it ever being 12DP!

Just using 67/4 (calculated by a very complex series of neural operations within my head, in less time than it takes to read it) gives me 16.75 and it is clearly slightly less than that.

All Topics | Latest Posts

Please login to post a reply.

Magazine Locator

Want the latest issue of Model Engineer or Model Engineers' Workshop? Use our magazine locator links to find your nearest stockist!

Find Model Engineer & Model Engineers' Workshop

Latest Forum Posts
Support Our Partners
Eccentric July 5 2018
emcomachinetools
Allendale Electronics
ChesterUK
EngineDIY
Warco
cowells
Eccentric Engineering
Subscription Offer

Latest "For Sale" Ads
Latest "Wanted" Ads
Get In Touch!

Do you want to contact the Model Engineer and Model Engineers' Workshop team?

You can contact us by phone, mail or email about the magazines including becoming a contributor, submitting reader's letters or making queries about articles. You can also get in touch about this website, advertising or other general issues.

Click THIS LINK for full contact details.

For subscription issues please see THIS LINK.

Digital Back Issues

Social Media online

'Like' us on Facebook
Follow us on Facebook

Follow us on Twitter
 Twitter Logo

Pin us on Pinterest