Myford 254 Apron Rebuild

[Lionel TitchenerParticipant @lioneltitchener]

Hello,

I've been lurking around this forum for some time, and now have a problem that members here may be able to help me with.

After running the saddle into the stop, the clutch did not stop a pin being sheared in the feed drive gear train in the apron.

After stripping it down I found some of the gears were badly corroded. Bought replacements from Myford except for one gear, the hand wheel pinion, no stock. The pinion is badly worn and impossible to measure accurately

It has 16 teeth.

Gear is about .998” or 24.4mm diameter

Width of gear .515” or 13mm

Length of shaft including gear 3.900” or 99mm

Diameter .550” or 14mm

It meshes with the larger gear on the Rack Pinion Assembly.

I am told by Myford the gears have a pressure angle of 14.5°, and are normally 20DP.

The large gear on the Rack & Pinion Assembly appears to be 18DP As the O.D. for DP 18 is close to what the gear measures, 2.766” Diameter. At 20DP is come out at 2.500”

Never needed to make any gears in the past so used Google to try and understand how gears are measured, hopefully I have got this correct.

This is what I have worked out.

48 Teeth and 2.766” diameter

Measure across 5 teeth is 0.771”

Measure across 4 teeth is 0.610”

So is the pitch 0.161”?

For 18DP Gear I get these results.

PCD. Teeth Divided by DP = 2.666” For 20DP 2.400”

OD. Teeth +2 Divided by DP = 2.777” For 20 DP 2.500”

Module. 25.4 Divided by DP So 25.4 divided by 18 = 1.41 For 20DP 1.27

No of Teeth PCD x DP So 2.666” x DP18 = 47.98 For 20DP 48

This leads me to believe that the DP is 18.

Therefore I need to find a 16 tooth 18DP Spur Gear either on a shaft, or a gear that can be pinned to a new shaft.

I’ve looked at HPC Gears, they do pinion gears on shafts but not one long enough.

Contacted **LINK** but not yet had a reply.

Anyone able to suggest where I can obtain a suitable part or get one made?

Thanks

Photo 1

Shows the Pinion next to the gear it meshes with, I have used this gear for my calculations as it is a new gear.

Photo 2

Shows where the gear locates, it’s not pushed all the way in it sits under the larger gear at about 4 o’clock.

All the four gears at the top of the apron are new, unfortunately Myford no longer stock the pinion with the small gear.

Photo 3

Pinion is part number 45 in the diagram.

[Lionel TitchenerParticipant @lioneltitchener]

[Neil WyattModerator @neilwyatt]

Hello Lionel,

I'm sure someone who can help will be along soon…

Neil

[John Stevenson 1Participant @johnstevenson1]

Lionel,

Your are correct in your calculations.

 

It has 16 teeth.

Gear is about .998” or 24.4mm diameter

Width of gear .515” or 13mm

 

So round that gear up to 1.000 as 2 thou on OD is neither here or there.

Add 2 to the number of teeth so 18 /1 = 18 DP.

 

Problem with HPC is they only do 20 degrees PA

 

One choice, if they do them is a gear off a Boxford@ 18 teeth as these are also 14.5 degrees PA.

Edited By John Stevenson on 01/03/2015 00:22:55

[Michael GilliganParticipant @michaelgilligan61133]

All seems fine and logical, except that the statement:

"Gear is about .998” or 24.4mm diameter"

is simply not true.

[hopefully, the .998" is correct]

MichaelG.

.

P.S. … I just found this page … Has anyone used them?

Edited By Michael Gilligan on 01/03/2015 07:14:45

[Lionel TitchenerParticipant @lioneltitchener]

 

 

Ah, Yes, I thought I would be picked up using dual measurements.

I didn't know if Myford originally designed the gear in Metric or Imperial.

It measures .998" But it also measures 25.4mm (1 inch) as you move around and measure in different locations.

I was not sure which is correct.

Thanks John for confirming my calculations, not had to work with gears before so spent the last few evenings using Google to try and understand how the calculations work. So far most of the catalogues only offer 22 degrees PA as you mention.

Also thanks to everyone that has taken the time to read such a long post.

I have been contacted by someone that can make me a gear.

Lionel

Edited for typo, catalogue changed to catalogues

Edited By Lionel Titchener on 01/03/2015 09:21:16

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Lionel Titchener on 01/03/2015 09:14:00:

Ah, Yes, I thought I would be picked up using dual measurements.

I didn't know if Myford originally designed the gear in Metric or Imperial.

It measures .998" But it also measures 25.4mm (1 inch) as you move around and measure in different locations.

I was not sure which is correct.

.

Lionel,

I wasn't picking you up for using dual measurements … merely remarking that your original 'conversion' was clearly wrong.

MichaelG.

[Lionel TitchenerParticipant @lioneltitchener]

Yes 25.4mm is .1000"

It was not a conversion, none of the dual measurement were done as a conversion, I just changed the vernier from imperial to metric to check measurements in both.

Sorry for confusion, if I implied it that way.

I thought maybe 25.4mm may have been used as outside diameter for a Module Gear, and 0.998" for a DP Gear.

John Stevenson put me right telling me to ignore the 0.998" and make it 1000"

No, I did not read your post as picking on me, been around enough forums not to worry what is said in posts.

Grateful for all your help.

Thanks,

Lionel

[Les Jones 1Participant @lesjones1]

No 25.4mm = 1.000"

Les.

[David JuppParticipant @davidjupp51506]

and 24.4mm is quite a bit smaller (approx. 0.961"   )   – I suspect simple case of misplaced finger when typing the post.

Edited By David Jupp on 01/03/2015 11:06:37

Edited By David Jupp on 01/03/2015 11:06:58

Edited By David Jupp on 01/03/2015 11:07:15

[Michael GilliganParticipant @michaelgilligan61133]

Posted by David Jupp on 01/03/2015 11:06:24:

and 24.4mm is quite a bit smaller (approx. 0.961" ) – I suspect simple case of misplaced finger when typing the post.

.

Which is exactly what I was remarking upon … but I had no idea whether it was the quoted .998" or the quoted 24.4mm that was in error.

MichaelG.

Edited By Michael Gilligan on 01/03/2015 12:13:31

[Lionel TitchenerParticipant @lioneltitchener]

 

Posted by Les Jones 1 on 01/03/2015 10:26:42:

No 25.4mm = 1.000"

Les.

You are correct I was having a bad day.

It should have been 25.4 in original post not 24.4

Edited By Lionel Titchener on 01/03/2015 20:20:24

[Chris Pearson 1Participant @chrispearson1]

Just in case anybody else has this problem …

In my case the pinion is acceptable, but the shaft is a little worn..

The tip diameter is 25.6 mm. The root diameter is 19.05 mm. It is module 1.5 with a 20 degree pressure angle.

Some of the other gears in the apron seem to be 20 DP and 14.5 degrees or at least they mesh with standard change wheels, but this one is clearly not.

[alan-lloydParticipant @alan-lloyd]

My book gives the part number as, 12035, its a 254 plus

[duncan webster 1Participant @duncanwebster1]

Posted by Chris Pearson 1 on 04/05/2019 15:40:36:

Just in case anybody else has this problem …

In my case the pinion is acceptable, but the shaft is a little worn..

The tip diameter is 25.6 mm. The root diameter is 19.05 mm. It is module 1.5 with a 20 degree pressure angle.

Some of the other gears in the apron seem to be 20 DP and 14.5 degrees or at least they mesh with standard change wheels, but this one is clearly not.

OP says the gear has 16 teeth, if the module is 1.5 then the OD should be (16+2)*1.5 = 27 mm

My metric 254 moves the saddle 25mm for one rev of the handwheel (checked with DRO), which suggests a circumferential pitch (or some clever gearing), but 6 teeth on the rack is 25mm which is a very odd CP

[Chris Pearson 1Participant @chrispearson1]

Posted by duncan webster on 04/05/2019 19:08:44:

Posted by Chris Pearson 1 on 04/05/2019 15:40:36:

Just in case anybody else has this problem …

In my case the pinion is acceptable, but the shaft is a little worn..

The tip diameter is 25.6 mm. The root diameter is 19.05 mm. It is module 1.5 with a 20 degree pressure angle.

Some of the other gears in the apron seem to be 20 DP and 14.5 degrees or at least they mesh with standard change wheels, but this one is clearly not.

OP says the gear has 16 teeth, if the module is 1.5 then the OD should be (16+2)*1.5 = 27 mm

My metric 254 moves the saddle 25mm for one rev of the handwheel (checked with DRO), which suggests a circumferential pitch (or some clever gearing), but 6 teeth on the rack is 25mm which is a very odd CP

OD = (N+2)*1.5 is only an approximation, which may be better for larger gears.

The pinion meshes with a 48 tooth gear which drives an 18 tooth pinion which meshes with the rack.

Funnily enough, the imperial rack measures 25.4 mm over 6 teeth. So one turn of the hand wheel turns the big wheel 1/3 of a turn, which equates to 6 teeth of the rack pinion.

It has been interesting fettling my 254. In many ways, they are very basic lathes, but they do seem to be well made. One exception may be poor lubrication of the handwheel shaft, but in the absence of oil, no lubrication system will work.

[duncan webster 1Participant @duncanwebster1]

"OD = (N+2)*1.5 is only an approximation, which may be better for larger gears."

well HPC, who actually make gears quote 16t 1.5 MOD OD = 27.00 mm

[Chris Pearson 1Participant @chrispearson1]

Posted by duncan webster on 04/05/2019 22:31:27:

"OD = (N+2)*1.5 is only an approximation, which may be better for larger gears."

well HPC, who actually make gears quote 16t 1.5 MOD OD = 27.00 mm

I take the point. If one calculates module = 4/9 x tooth depth, the result is 1.46.

In theory, as Duncan points out, the reference diameter is 24 mm with a tip diameter of 27 mm and a root diameter of 20.25 mm so the scale of the pinion has been reduced by a factor of about 5%.

I found out today that this pinion was routinely replaced during refurbishment, which probably explains why they are in short supply as well as being, perhaps, a weak point.

[Dave Sawdon 1Participant @davesawdon1]

I need to remove and dismantle the apron on my 254S and, although this is a rather old thread, it seems that there are a couple of people here who have ploughed the same course before me … any advice on how to tackle the job would be gratefully received.

Dave

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