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Cast Iron For Boxford Change Gears?

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William Chitham21/05/2019 12:15:16
12 forum posts

I have set myself the task of making a 127/135 compound gear for my Boxford and am considering material selection. I think the existing change gears are cast iron and I have been advised that SG(GGG40) would be suitable. Two questions before I order: can anyone suggest a more economical alternative (some grade of steel plate maybe?) and if it is to be SG what are my chances of getting two 3/8" thick gears out of 1" of round given that I don't have a bandsaw or powered hacksaw?

Thanks, William.

Bazyle21/05/2019 13:16:39
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4542 forum posts
184 photos

Changewheels shouldn't be under a lot of stress so you can use tufnol sheet, maybe with a nice brass hub. Delrin is another possibility, or some reinforced plastic and of course aluminium.

Steel, ordinary mild type is best avoided as it will be far more wearing on your cutter and will be noisy in use, especially a large one.

Is your leadscrew metric? As far as I remember the 127/135 combination is to do imperial gears on a metric lathe. 100/127 is the normal set for imperial lathes.

Clive Foster21/05/2019 13:17:58
1713 forum posts
46 photos

Delrin would be up to the job and far easier and cleaner to machine than cast iron. I guess £10 - £20 worth of 10 mm thick sheet would do. Fairly easy to obtain from E-Bay or other sources.

Clive

duncan webster21/05/2019 13:26:44
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2083 forum posts
32 photos

If you must have iron, then I don't see why you'd need SG iron, ordinary grey cast would be strong enough. You don't mention the finished diameter, but I'd pay the supplier to cut 2 pieces 1/2" thick rather than risk trying to cut it yourself.

Nigel Bennett21/05/2019 14:20:06
287 forum posts
6 photos

If you've set yourself the task of doing it, fair enough, but this chap advertises plastic ones on eBay and I had a couple off him for my Boxford 280. Usual disclaimer; I've been very happy with them.

I can't find exactly what you're looking for, but here's a sample:

**LINK**

Suggest you contact him and ask for a price for what you need.

Brian Wood21/05/2019 18:06:08
1895 forum posts
37 photos

Hello William,

Nigel Bennett suggest a combination 64/54 delrin gear as a translation gear. The material will I'm sure do well for your needs, BUT be careful over specifying the tooth count if you are following up on his link

Boxford 280 lathes come with either 6 mm or 4 tpi pitch leadscrews, yours might be 3 mm as would seem to be the case with a 135/127 translation gear and a better fit to your needs would be with 68/64 for a leadscrew of that pitch.

There is an error over the pukka conversion which amounts to 0.05 mm in 100 mm of thread, per turn of the leadscrew.

Doing the maths, 135/127 = 1.06299 where 68/64 = 1.0625. There isn't another choice available either I'm afraid

Regards

Brian

 

Edited By Brian Wood on 21/05/2019 18:07:20

Bazyle21/05/2019 18:26:13
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4542 forum posts
184 photos

The 280 probably has module gears whereas you CUD has 18DP 14.5PA gears as you probably know. I'd also expect a CUD to be imperial leadscrew. Unless you are intending to cut a new cross-slide screw and be fussy about it you don't need the accuracy of an exact conversion. (a lot of Myfords have an inaccurate cross slide from new and their owners don't know it. One of our club members found out when he treated himself to a new one and found the parts he was milling did not match the ones he had made before and it wasn't due to the wear)

DC31k21/05/2019 20:41:17
11 forum posts
Posted by Brian Wood on 21/05/2019 18:06:08:

Doing the maths, 135/127 = 1.06299 where 68/64 = 1.0625. There isn't another choice available either I'm afraid

There are in fact three other choices available that give better approximations than 17/16 (or its multiples). 84/79, 101/95 and 118/111.

While none of these are common gears, to say that nothing else is available is not correct.

In any discussion of change gears, the many continued fraction calculators available online for free are an invaluable resource.

Richard -21/05/2019 21:45:45
37 forum posts
4 photos

If you look at the lathes UK website there is a calculator, it allows you to input your available gears and give you combinations with percentage errors. This allows you to make an informed choice. My CUD now sold had a metric lead screw, I used to cut imperial threads successfully using this method.

Richard

Brian Wood22/05/2019 09:00:22
1895 forum posts
37 photos
Posted by DC31k on 21/05/2019 20:41:17:
Posted by Brian Wood on 21/05/2019 18:06:08:

Doing the maths, 135/127 = 1.06299 where 68/64 = 1.0625. There isn't another choice available either I'm afraid

 

There are in fact three other choices available that give better approximations than 17/16 (or its multiples). 84/79, 101/95 and 118/111.

While none of these are common gears, to say that nothing else is available is not correct.

In any discussion of change gears, the many continued fraction calculators available online for free are an invaluable resource.

You are of course quite right, I was being a bit economical with the truth, but in my defense I would suggest that for most joining threads or short couplings of say 25 mm in length, the 17/16 approximation and it's multiples, will make quite adequate joints with tolerable errors, and from wheels of sensible sizes.

The alternative combinations all include awkward primes and the last at 118/111 is perhaps a lot of work to make, you might just as well go the whole hog at that stage for 135/127

I'm sorry to have misled people

Regards Brian

 

Edited By Brian Wood on 22/05/2019 09:01:14

Micky T22/05/2019 10:57:25
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48 forum posts
28 photos

Hi William I made my 100/127 conversion wheel from Aluminium with a brass bush in the centre

77d3fdd2-c361-458f-b117-31c0f9e9aff2.jpeg

Mickyt

William Chitham24/05/2019 17:11:40
12 forum posts

Thanks for all the replies, all very helpful, the gears are to do imperial on a metric leadscrew Boxford CUD. I do have one of the 54/64 gears from that ebay seller, works ok and nice guy but I have become somewhat obsessed with the whole business of gear trains and am determined to make my own 135/127. I have been using NthreadP to test different combinations and 127/135 it has to be. Aluminium looks nice but v expensive, Delrin looks good for first attempt, I can get enough for three or four blanks for the price of two in cast iron. Still a long way from cutting though as I haven't decided how to do the indexing yet, CNC, or some kind of home brew mechanical. How did you do yours Micky?

William.

larry phelan 125/05/2019 10:22:34
421 forum posts
11 photos

With sound advice from Brian Woods, I made a pair of gears from Aluminium ,just for the experience.

They worked out perfectly, now all I need is to find a use for them !!

Still ,my aim was not "What for " but "How to ".

My thanks again to Brian .

Micky T25/05/2019 10:56:45
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48 forum posts
28 photos

I made an Arduino indexer as described in MEW 249. There was a thread about slight changes to get the package working **LINK** . I then used the Arduino code from the home model engine machinists forum **LINK** . Well worth the read and probably the easiest way to index a 127 gear.

Mickey

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