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Myford Super 7 QC gearbox Mk1 problem

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brian goodison02/04/2022 13:36:46
9 forum posts
10 photos

Hi Guys, a newbie here, I’m looking for some advice/tips from any experienced Myford experts.

I have a Super7 fitted with an early Mk1 QC Gearbox # 2281 (short lead-screw driven from right hand side of gearbox with three external gears)

The gearbox selector internal tumbler gear is damaged so needs replacing, I believe this tumbler gear is the same as the later MK2 gearbox (39 teeth) can anyone confirm this?

Consequently I have few questions.

Do I have to completely remove the gearbox from the lathe in order to get to the tumbler and replace it?

There is very little access so do I have to remove the other gear clusters as I cannot even see how the tumbler gear is held to the selector shaft?

Would it help just remove the top set of gears?

Any tips on stripping the gearbox and pitfalls to avoid?

I have downloaded the gearbox manual from the files but it appears to be for the MK2 Gearbox and does not give information of how to access and replace the tumbler.

So if any of you guys have replaced the tumbler I would appreciate any insight and tips on tackling the job.

Thanks in advance for any help and sorry for long post. Regards Brian.

Simon Williams 303/04/2022 08:53:49
659 forum posts
82 photos

<BUMP>

Anyone got a copy of the older model gearbox drawings?

I'm out for the day - but I think I've only got the newer document anyway.

Rgds Simon

ega03/04/2022 09:57:58
2543 forum posts
201 photos

If you end up dismantling the box to any great extent be sure to get the cone of 16 to 32 teeth gears back in the right order (that point was the only issue when I did my Mk2 box; I have no experience of the Mk1).

Buffer03/04/2022 10:23:42
338 forum posts
153 photos

Brian I had to change the main splined shaft on my gearbox so it had to all come apart. I can't remember specific details but I do remember that it wasn't hard to get apart and back together again. It's a very basic gearbox and honestly you should have no problem pulling it apart and putting it back.

john fletcher 103/04/2022 10:55:14
794 forum posts

Hello Brian can't remember any problems when I changed a broken gear 30 odd years ago. Myford didn't have the gear available any more, I got one from HPC gears at Chesterfield it had all the correct details except the bore, which was to big. I had to sleeve it. John

brian goodison03/04/2022 12:31:26
9 forum posts
10 photos

Thanks for the replies so far Guys,

Ega, tks for tip.

Buffer, I think I should be ok stripping and refitting as my back ground is in the motor trade so know my way around gearboxes but it’s always helpful to gets and advice from those who have been there previously.

John, I had to also replace the three external gears which I got from HPC, the gears all had to be modified, one with a bush, the other two needed key-ways and all had to be shortened…..not a cheap exercise as HPC did all the modifications.

I have now turned my attention to the gearbox internals, hence my questions, both the Myford site/Ebay list a tumbler gear (39T) for the Mk2 gearbox which I hope is the correct gear, I was hoping someone could confirm it is the same as the Mk1 tumbler gear.

**LINK**

Brian.

Brian Wood03/04/2022 20:35:00
2567 forum posts
39 photos

Brian,

Sticking my neck out, but the gearbox internal ratios are the same for both versions and the layout is the same. I can confirm that the tumbler gear is 39 teeth, the gear itself runs on a captive pin in the selector carrier so the odds favour a 39 T gear in the early design.

The changes made with the Mk II gearbox were hardened gears, dog clutches and taking the leadscrew right thought to a 26/52 reduction gear on the change wheel side. Only the 26 T gear of that pair was hardened. This dispensed with the cluster gearing in the blister cover on the early boxes.

I can't help with strip down notes though having been spared the need but I don't think you need to take it off the lathe to do so. If you can find him in the Forum pages, John Haythorthwaite had to go through it.

Regards

Brian

brian goodison04/04/2022 13:22:33
9 forum posts
10 photos

Thanks Brian for the reply and confirming the internals and 39T tumbler are the same, I found this video which shows a Mk1 box been rebuilt which looks useful, https://www.youtube.com/watch?v=ZgrcigBIfVM it does look as though I need to remove all the gears and cover plates from the left hand end of the lathe which is something I was hoping to avoid so will probably end up removing the gearbox.

The video shows the tumbler has taper pins which have to be removed so hope these don’t cause a problem removing them and they are available.

Regards Brian.

Brian Wood04/04/2022 14:21:39
2567 forum posts
39 photos

Brian,

One tip I recall is to turn the selector carrier over to gain access to the narrow end of the taper pins so that you can drive them out. It probably needs one of the shafts to be withdrawn to be able to do so.

A way you can confirm the idler gear tooth count is to use the formula DP = (n+2) divided by outside diameter. If you can establish the gear diameter [inch measure], the DP value for those gears is 20 and 'n' is the tooth count

Assuming I am correct at 39 teeth, the gear diameter will be 2.05 inches. I hope that helps you

Regards

Brian

brian goodison04/04/2022 15:51:07
9 forum posts
10 photos

Thanks Brian, that’s a very useful formula, I was under the impression that Myford gears had a DP of 14.5 and consequently when I replaced the three external drive gears I replaced all three as a set (although only two were damaged) see my album.

The new HPC gears were 20DP and having now checked the original gears they appear to be 20DP …….I could have saved a bundle of cash as apparently I only needed two!sad

noel shelley04/04/2022 16:35:34
1353 forum posts
21 photos

14.5 is the pressure angle - I think ! Not all myford gears are 20dp, the back gear is 16dp. Noel.

DMR04/04/2022 17:36:28
127 forum posts
14 photos

The guts of the Mk1 are identical to those in the Mk2; only the external gears are different. Note that it is not sensibly possible to convert the Mk1 to be a Mk2. I think you will need to remove the box to remove the Lay Shaft to get at the taper pin on the 39T shaft. No reason to not us the same taper pin again; just get all the tapers the right way round or it will work loose. Your external gears got broken because you don’t have the aluminium cover over them. It helps stops swarf and the saddle running into them. It is possible to fabricate a replacement and I can give you pictures if it helps
Dennis

Brian Wood04/04/2022 18:08:30
2567 forum posts
39 photos

Good set of pictures Brian, very helpful

I confirm that the gearbox gears will all be to 14.5 degree pressure angle, but the gears that HPC have supplied will all mesh well together being in an isolated cluster.

If you haven't changed the 18 T gear on the leadscrew I suggest you do so, it is not good practice to run worn gears with new and especially so in this case as you would have two different pressure angle running together and the trio will suffer as a result.

Finding a 39 tooth tumbler gear in 14,5 degree PA might be difficult but I have a suggestion if the gear runs well on it's captive pin. Have an engineer turn off the remainder of the teeth and fit a thick Phosphor bronze collar securely to the rim and cut the new teeth into that. It will be perfectly satisfactory, bronze runs well with ferrous

I salvaged an otherwise good gear tumbler body on a 1904 Hendey lathe where all the teeth had been worn down to stumpy apologies, all the others in the gearbox I had made new or reformed where possible and I especially wanted to preserve the pin/gear fit rather than match that. Those transfer gears work hard as they are the central element in any gearbox selection

I would happily do the job for you but I am struck down with shingles in the right eye and it might be while before I feel like spending time in the workshop again.

I hope you can get sorted out satisfactorily

Regards Brian

Simon Williams 304/04/2022 19:03:55
659 forum posts
82 photos

Shingles...

Oh dear Brian that's a rotten stroke of misfortune! I/m sorry to hear that you have found yourself suffering that turn of events. My wife had shingles in her thigh/hip some while ago - your misfortune is not alleviated by my rehearsing her tribulations but I do sympathise.

Do get well soon.

My very best wishes

Simon

Brian Wood04/04/2022 19:51:24
2567 forum posts
39 photos

Thank you Simon. I have seen others thus afflicted and judge myself in better shape than those poor unfortunates; It is a wretched condition in whatever strength of attack and your sympathy is very much appreciated.

Funny how this Mk I gearbox brings us into contact at odd intervals isn't it?!

My best wishes

Brian

brian goodison05/04/2022 11:27:13
9 forum posts
10 photos

Thanks Dennis (DMR) for your thoughts and confirming the gearboxes are internally the same, also for the offer of gear cover dimensions, I do have the gear cover and it was in place but was just not in the pictures I posted. I have posted another picture showing it as I had moved it further down the lead screw to give better access to the gears while I removed them.

brian goodison05/04/2022 11:28:43
9 forum posts
10 photos

Brian, sorry to hear you are not well, my wife had shingles several years ago but seemed to get over it and it has not recurred, hope you feel better soon.

I will use the HPC 18T lead screw drive gear when eventually I get the lathe sorted, I may as well as they are a set. As regards the 39T tumbler, from the replies that say it is the same as the Mk2 gearbox I think the one that Myford supply (as per the link I posted) should do the job, so once I get it out and providing it’s the same I will probably use it.

I appreciate you saying that you would sort it for me and if the Myford gear doesn’t work out could I get back to you….obviously when you are feeling better.

How you describe repairing the gear is way-way beyond my pay grade, I only learned basic lathe work at night school about a hundred years ago!

Best Regards Brian.

Brian Wood05/04/2022 12:10:46
2567 forum posts
39 photos

Brian,

Just a word of warning with buying the spare part from Myford, I just hope they haven't switched entirely to sourcing all their spares from China.

I would quiz them hard to be sure it will be suitable for the Mk1 gearbox, play the novice card, you don't want a gear made to modern standards!

I am sorry about the accident in timing here and you are certainly very welcome to come back to me if you feel the least bit concerned over buying a straight replacement. This wretched business can't last forever and I will get back into the workshop.

Send me your email address in a PM and we can remain in contact that way. I can then send you some pictures of the Hendey gearbox repair, it was a total wreck and the PBr work was just a part of the job

Best wishes and good luck

Brian

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