lost drive to power feed

[Mark GuyParticipant @markguy26995]

[Mark GuyParticipant @markguy26995]

[Mark GuyParticipant @markguy26995]

The drive to the worm gear from the motor is only with a grub screw so I am surprised it has taken the gears rather than spin the screw. May be because I was in the slowest speed on the change gears

[Howard LewisParticipant @howardlewis46836]

From the toothcounts and ODs provided, my guess would be that the gears are 20DP.

If my guess is correct, you will need to turn up blanks, the one for the 21T will be 1.150" diameter, and that for the 42T, 2.200" diameter

Since they only mesh with each other, it would not matter if the Pressure Angle differs from all the others.

Exactly matching gears "off the shelf" may be hard to find, or be expensive and still require modification to become exact replacements.

To make new gears you will need two Brown and Sharpe cutters. A No. 5 for the 21T and a No. 3 for the 42T

It looks as if both are plain bores (A bush in the 42T ) so although you may need a keyway in the 21T, you will be spared the need to cut splines.

The good news is that being feed gears, if you can still feed manually. With a Rotary Table or Dividing head, you should, be able to turn up the blanks in the lathe, and then cut the teeth on the mill.

Once up and running again, you will have gained more experience and confidence in you engineering activities.

Howard

[DC31kParticipant @dc31k]

Posted by Mark Guy on 20/12/2020 18:18:12:

The larger gear is 2.164 with 42teeth and the smaller would have been had it had teeth 1.055 with 21teeth. yes the 2 sheared gears only mesh with each other. The shaft centers would be difficult to measure as the are on different housings. But a I’ve calculated they would 1.500.

OK, the three dimensions do not agree.

A 42t gear of 2.164" OD is 20.3 DP, a non-standard size.

A 21t gear of 1.055" OD is 21.8 DP, a non-standard size.

63 teeth of gears on 1.5" shaft centres is 21 DP, again non-standard.

Have a really good measure of the three distances and see if you can come up with some numbers that will translate into standard gears.

The more standard they are, the easier it will be to find replacements. It is good that they only mesh with each other – that way the question of having to determine a pressure angle is irrelevant.

The grub screw in the worm should have a brass pad under it. The shaft should be smooth, not dimpled. The idea is that any bind up overcomes the friction between brass pad and steel shaft.

This might not be relevant to you, but have a really good look at the gears and sleeve between them you show in the plan view. On the later machine, the gears differ by one tooth (so at a casual glance, they look identical) and if you put the wrong one onto the leadscrew first, problems arise later on in the assembly process.

The centre distance for the 20DP size suggested above is 1.575" so if you can find a way of accurately measuring that, it would be good confirmation and make life much easier.

Edited By DC31k on 20/12/2020 19:29:29

[Pete RimmerParticipant @peterimmer30576]

2.164" is almost exactly 55mm that makes it work out perfectly as a 1.25 MOD gear.

The 21 tooth should be 28.75mm dimeter and the centre distances should be 39.375mm supposing they are not profile shifted.

If you can give me the centre distances VERY accurately I can make both for you. The only concern I have is the big gear looks to have a bushing pressed into it, which usually means it engages with two gears. Is that the case?

[not done it yetParticipant @notdoneityet]

Deleted.  Sorted in an earlier post🙂

Edited By not done it yet on 20/12/2020 19:50:13

[Howard LewisParticipant @howardlewis46836]

Sorry to disagree Richard, but 23/ 20 = 1.15 OD = (Teeth +2 )/DP according to Ivan Law 

Since it looks as if only one tooth is broken from the 42T gear, it ought to be possible to get an accurate OD.

Can other gears be measured? It would seem unusual to mix DP and Module gears in one machine, from the factory

So other gears may confirm the tooth pitch

All the dimensions need to be accurate so that Pete Rimmer's kind offer can produce the correct gears whether 20 DP, or 1.25 Mod.

It would be disaster to fit new gears only to find that they are of the wrong pitch, and either have zero or excessive backlash because of the centre distance.

Howard.  GRRRR Smileys!

Edited By Howard Lewis on 20/12/2020 20:05:12

[Mark GuyParticipant @markguy26995]

Hi Pete I’ve been thinking with the big gear with only 1 tooth missing would it not be easier to weld it up and re cut it? As for the small gear the only way I could get a measurement was from the bottom of the broken gear in the trough then add the depth of the 42 tooth gear which was .090. This was a quick measurement I did just to give a size to reference to if any one had a box in bits.

[Howard LewisParticipant @howardlewis46836]

According to Ivan Law's book, the depth of cut for a 20 DP gear would be 0.108"

For a 1.25 Mod gear it would be 2.70 mm or 0.106"

Don't know if this helps you with the dimensions of your gears, and determining whether 20 DP or 1.25 Mod.

Has anyone a manual / Spare parts list which can throw any light on the subject?

Howard

[Pete RimmerParticipant @peterimmer30576]

Maing a new gear is easier.

For 1.25 mod gears the base diameters should be 1.942" and 0.971"

For 20DP they should be 1.973" and 0.987"

That is if neither are profile-shifted. What is your measurements across the bottom of the tooth gaps? You'll have to do a best-effort for the 21T seeing as it's an odd number and small diameter to boot.

[Mark GuyParticipant @markguy26995]

Just re calculated the small 21 t as 1.0785

[Mark GuyParticipant @markguy26995]

Sorry My mistake the small gear is only 20 teeth and I’ve checked and checked them both again 20 and 42 teeth

[Pete RimmerParticipant @peterimmer30576]

Posted by Mark Guy on 20/12/2020 21:19:11:

Sorry My mistake the small gear is only 20 teeth and I’ve checked and checked them both again 20 and 42 teeth

Thank gawd for that I was going a bit crazy with those numbers.

These are 1.25mod gears. Measure every dimension and I'll knock them out for you. You will have to give me centre distance as close as you can measure it. It should be 1.526"

[Mark GuyParticipant @markguy26995]

Pete the 42 tooth is a double gear but only one side damaged

[Pete RimmerParticipant @peterimmer30576]

Nothing's ever easy is it? Are the gears each end completely identical?

[DC31kParticipant @dc31k]

Posted by Pete Rimmer on 20/12/2020 21:35:54:

Nothing's ever easy is it? Are the gears each end completely identical?

There is enough depth below the teeth of the big one to turn the old teeth off plus a good bit extra and shrink or loctite or Dutch key a large-bored new one on.

The only thing to watch out for is if it is necessary for the teeth of the two to be timed/clocked to each other.

Easiest way to confirm centre distances if it is difficult to do a direct measurement is to turn up two discs that are the pitch diameter of the two gears and bored to the correct measurement. Install on their shafts. If they interfere, the PDs are too big. If there is an excessive gap, the PDs are too small.

Edited By DC31k on 20/12/2020 21:58:53

[Pete RimmerParticipant @peterimmer30576]

Yes a scotch/Dutch key would be a good way of fitting the replacement gear to the hub and there's plenty of room for it. I see no reason why the teeth would need to be timed in a power feed gearbox so that should be no issue IMO.

[Mark GuyParticipant @markguy26995]

I don’t think they are timed but I will have a look tomorrow evening and check

[Pete RimmerParticipant @peterimmer30576]

Posted by DC31k on 20/12/2020 21:54:34:

Easiest way to confirm centre distances if it is difficult to do a direct measurement is to turn up two discs that are the pitch diameter of the two gears and bored to the correct measurement. Install on their shafts. If they interfere, the PDs are too big. If there is an excessive gap, the PDs are too small.

That'll work if directly measuring isn't feasible.

Pitch diameters should be 2.067" and 0.984"

[Mark GuyParticipant @markguy26995]

I think there is enough material left on the stripped gear to just mesh it the larger one, measure inside to inside then add the spindle size?

[not done it yetParticipant @notdoneityet]

If these gears happen to be 20DP, would not change gears by myford suffice as replacements?

Edited By not done it yet on 21/12/2020 07:06:55

[Mark RandParticipant @markrand96270]

I need to check in the shed, but it's just possible that I might have a set that could sort you out.

My Mk1 VBRP had a burnt out feed motor and cracked gearbox casting when I got it, but I managed to buy a replacement gearbox and motor from a pikey* who was changing his machine over to single phase with one of the nasty bolt on feed drives.

I think I've still got the original gearbox under a bench, so If I can find it, I can liberate the gears from it and post them to you.

If I can't find the box, then they're either 20DP (same as the changewheels for the box), which would be available from HPC-gears or they're 22DP, which are mich more rare in the UK.

 

*The sod charged me extra for the motor, even though it's an integral part of the assembly…

Edited By Mark Rand on 21/12/2020 09:52:02

[Pete RimmerParticipant @peterimmer30576]

That's handy – saves me making them!

When will you know Mark? I have time right now if I have to make the gears but I won't have in the new year when I go back to work.

[Mark GuyParticipant @markguy26995]

That’s sound mark cheer. Did you have any trouble getting the keyway on the lead screw shaft to line up with the key in the forward/reverse dog drive on the right side of the bed

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