Chuck backplates, buy or make?

[Andrew TinsleyParticipant @andrewtinsley63637]

[Andrew TinsleyParticipant @andrewtinsley63637]

I have 5 chucks that need backplates for use on my ML7 refurbishment project.

I note that Tracy Tools do a tap for the Myford backplate thread for not a lot of cash. Now I have done hundreds of tapped holes over the years, but never anything near as big as this!

Now 5 backplates ready tapped will cost well over £100, while the tap is around £20 from memory. Providing I can get the raw material at a reasonable price (steel or cast iron ?). It may make economic sense to make my own backplates.

I suppose it depends on the cost of the raw materials. What do the experts think

[Nick_GParticipant @nick_g]

.

I would say the economics would equate to buying them. ………….. Unless. ……….

Unless that is you have a place local to you that can supply the raw material and you can actually pick it up yourself. – I say this as the postage costs of the material will be a killer.

Nick

Edited By Nick_G on 20/12/2016 20:06:44

[roy entwistleParticipant @royentwistle24699]

I would suggest that the spindle thread should be cut on the lathe rather than using a tap. I think that you might have problems keeping a tap that size square and the torque required must be enormous

[Chris Evans 6Participant @chrisevans6]

At that price the tap will be carbon steel and may not last for five back plates. I once bought a 5/8" 26 TPI carbon steel tap set that did not complete one hole so it is HSS every time for me now. If you do want to make them and have a local enough cast iron foundry then make some patterns (MDF is fine) and get them cast. Cut the threads on the lathe and use a tap to tidy the form.

[John ReeseParticipant @johnreese12848]

Posted by roy entwistle on 20/12/2016 20:09:15:

I would suggest that the spindle thread should be cut on the lathe rather than using a tap. I think that you might have problems keeping a tap that size square and the torque required must be enormous

By all means cut the thread on the lathe. Once the threads are nearly to size a tap can be used for the finish pass.

[michael pottsParticipant @michaelpotts88182]

Buying a backplate is alright if someone stocks the size and thread that you need. I have to make a backplate for a chuck to go on my Myford Speed 10. I will make that, though they are available. I also have to make one for a Perris PL100 lathe. That has a 1/2" BSF thread which is not available. I made one for a Perris SL90 lathe with a 1/2" UNF thread, also not available. That came out Ok, using the lathe to cut the thread and finishing with a tap. Sawing these things out of cast iron bar is hard work, though the Myford one is already cast and just needs a lot of machining. A job for the spring when it is a bit warmer.

[Brian OldfordParticipant @brianoldford70365]

Posted by John Reese on 20/12/2016 20:28:39:

Posted by roy entwistle on 20/12/2016 20:09:15:

I would suggest that the spindle thread should be cut on the lathe rather than using a tap. I think that you might have problems keeping a tap that size square and the torque required must be enormous

By all means cut the thread on the lathe. Once the threads are nearly to size a tap can be used for the finish pass.

My thoughts entirely. Use the tap to remove just a few thou'; almost like a chaser. The really really important bit is to get the register as close a fit as possible without binding.

[RobboParticipant @robbo]

Andrew

It is most feasible to bite the bullet and buy the backplates ready to use.

At around £20 the tap will be carbon steel, as has been said, an HSS tap will be in excess of £50.

However, cutting a thread this size by hand using just a tap isn't a practical proposition. You need to cut the thread on the lathe, at least for most of it, and finish with the tap. More important is to cut the register to a precise fit, and the ready made will be OK for this.

[Andrew TinsleyParticipant @andrewtinsley63637]

Thank you gentlemen!

I am glad you told me to cut the thread in the lathe. I must admit to being almost brain dead to even think I could tap it! That is precisely why I use the beginners forum. I don't mind making a fool of myself here! I think I shall purchase the backplates, I am not sure I could get the register absolutely correct.

Just as a matter of interest, why does everyone use cast iron for backplates? There must be a good reason, but right now I can't think of one.

Thanks everyone,

Andrew.

[MWParticipant @mw27036]

 

Posted by Andrew Tinsley on 20/12/2016 22:36:59:

Thank you gentlemen!

Just as a matter of interest, why does everyone use cast iron for backplates? There must be a good reason, but right now I can't think of one.

Thanks everyone,

Andrew.

Hi Andrew,

Yes, I don't know what tap size myford is but it certainly sounds a lot bigger than a sherline spindle nose!

Threads over a certain size were never meant to be tapped free hand, the only way you can do huge sizes no lathe involved is serial taps that slowly cut to the full diameter, but even then we're talking maybe 5 or 6 taps. So the lathe is the most sensible way to go about it, I could only think of a few exceptional cases where it was simply impossible to mount the "thing" in the lathe. Even then on a big assembly, you'd preferably partition the assembly off for where you needed said thread.

So, as to why is cast iron good for a backplate, it's generally the same material as the chuck, which obviously has it's own plusses. But i'm guessing you're asking why we can't use a softer material like aluminium or even similarly hard material like steel.

Answer to the first part is precisely because it's too soft, you wouldn't be making something that would last very long, the aluminium would probably start to get banged up over the years. Every time it may run the risk of burring up especially if the fit is so tight you need a soft hammer to loosen it up. Why would you want to do that I don't know.

Another reason why is because iron is a very good load bearing material for vibration, it takes up noise generally speaking, I know this because I changed from aluminium pulleys on my machine, to cast iron ones and the difference is markedly so.

Second part, why don't you use steel? Well, this isn't as easy to answer, because in theory you could and in theory it would obviate all the above problems, but then when we get down to economics, where are you going to find a BMS bar 125mm Dia? and more importantly, how much of it do they want you to buy in order to pay for the job?

 A slight exaggeration in some cases but cast iron is a relatively cheap way of making big sized things and it machines well, cast steel on the other hand, is a total pig, hence why you don't come across it very often.

Michael W

Edited By Michael Walters on 20/12/2016 23:21:39

[JohnFParticipant @johnf59703]

Hi Andrew, Sorry I've not had time to read every post so apologies if I cover ground already covered .

My advice would be make your own — the reason is I have tried on several occasions purely from economics or speed to purchase backplates or chuck adaptors to use my chucks [Myford] on rotary tables et al but they all fall short on tolerance being 3 to 5 thou oversize on the register bore or undersize on the register for adaptors.

This wil not give satisfactory results, you ask how to measure the bore when making your own, well in the absence of a precision bore mic make a plug gauge and turn the first 0.100 or 0.150 length of the gauge to say 0.001 undersize so when this fits you know you are very close to the final size. Depends on the kit you have but this method will give you the desired accuracy with just a vernier or digital calliper to assist in getting close to what you want.
Same with the thread make a plug gauge using the 3 wire method, use the wires on your lathe spindle to take a measurement and then make a plug gauge to this size plus a thou

Regards John

[John Stevenson 1Participant @johnstevenson1]

Arceuro sell a high quality HSS tap for Myford spindle noses.

Part # 060-101-00200

Been to the factory where they are made, state of the art gear used.

[Bill PudneyParticipant @billpudney37759]

Just a little background, sometimes it's good to remember why things are the way they are.

Going back to night school during my apprenticeship….."Cast iron was seen as a way of making things cheaply. It was also a way of making things that would not otherwise be possible. Cast iron was one of the reasons that the Industrial revolution happened"

The fact that it had some other advantages (e.g. vibration damping) wasn't discovered until later.

cheers

Bill

[Perko7Participant @perko7]

I made up a backplate using a lump of forged steel that was a blank for a flanged high pressure pipe connection. It was pretty hard stuff but machined beautifully and has a nice shiny finish that doesn't seem to tarnish.

[HopperParticipant @hopper]

You can buy unmachined cast iron blank backing plates from various places. (Or make a simple pattern and get some cast at your local foundry). It's then a simple matter to machine them up on the lathe they will be used on. Standard procedure is to clamp the blank to the faceplate, bore, then turn the thread and register recess in one setting, then flip it round, screw it on the lathe spindle and finish off the chuck mounting side in situ.

The thread does not have to be a super precision job. It's purpose is for retaining the plate only, not locating it. Locating is 100 per cent down to the register collar and matching recess. Indeed many spindle threads are deliberately made an undersize sloppy fit (relatively speaking ) to make sure they plate can move about sufficiently to ensure the register collar and recess do 100 per cent of the locating.

Edited By Hopper on 21/12/2016 06:16:44

[D HannaParticipant @dhanna35823]

Posted by Andrew Tinsley on 20/12/2016 22:36:59:

Thank you gentlemen!

Just as a matter of interest, why does everyone use cast iron for backplates? There must be a good reason, but right now I can't think of one.

Thanks everyone,

Andrew.

How's the resto going Andrew!

With the steel backplate I'll go back to my early days in the NSW Railways. One machine shop had made steel back plates for a few older screwed spindle lathes (TWINK brand from memory around 8" x 40" size) and those chucks were absolute pigs to unscrew especially if someone assembled them without lubrication and they were on for a while. Very prone to pick up on the steel to steel contact. Cast iron of the continuous cast type maybe 4E is great for machining if you can get hold of it.

DH

[not done it yetParticipant @notdoneityet]

My take.

The thread, while obviously a large part of the job, is nowhere near as important as the register. It can even be a bit loose, as long as it holds the back plate (and chuck) in position safely and securely.

The register is, by far, more important than the thread and accuacy is paramount for this aspect of the job.

The spigot for the chuck is also an important feature, which will need cutting accurately on y

our lat

he.

I would be requesting confirmation of accuracy before purchase and then measure carefully before accepting the items for use. (See above re accuracy of some purchased items) JohnF may well be right on that point.

You don't give any indication of sizes required. I note that Arc items, in steel, cost less than £100 for five, delivered (sizes 5" and less).

In your circumstances, buying in is the better option IMO, what with your admitted inexperience (good on yer!). I consider you have made the right decision. Perhaps buy in most and make the odd larger one as an experience exercise – it could always be used as a drive plate for turning between centres, if it were not quite good enough as a backplate.

[HopperParticipant @hopper]

BTW, why do you need five chucks? One good three jaw and one good four jaw should do the job, should it not? Two ready made back plates might be much more affordable.

[Ian S CParticipant @iansc]

If you buy in, regardless of the finish it will require to be faced square before fitting the chuck.

About twenty years ago I needed a back plate for a 6" 4 jaw chuck, I went to a profile cutting firm and bought a 200 mm X 50 mm hole, well they wanted the hole, and I wanted the bit that fell out, payed scrap price, can't remember may have been NZ 50 cents a Kg. Quite a few hours of lathe work later I had a back plate made from hot rolled steel. I was a bit worried about the steel to steel contact as my lathe has a screwed nose, but there has been no problem as yet, maybe different steel grades help here.

Ian S C

[Martin ConnellyParticipant @martinconnelly55370]

Hopper, I have 3 chucks. One good 4 jaw independent, one 3 jaw that only has the standard jaws, one 3 jaw that only has the reversed jaws and soft jaws. If I did not have the chuck with the soft jaws already I would probably have bought a chuck that had soft jaws as an option. The option of buying new standard or reversed jaws for these old chucks is not available

I have a threaded spindle nose for which purchased back plates are not available so making my own is the only option. Had to make a faceplate to suit as well. This doubles up as a catchplate.

I did make a backplate for someone else just so they could get running with an old lathe. By making it slightly tight and from cast iron they could scrape it to fit. I think any other material would have been harder to scrape to fit. They were not close enough to trial fit and machine again.

Martin

[HopperParticipant @hopper]

Posted by Martin Connelly on 21/12/2016 08:33:53:

Hopper, I have 3 chucks. One good 4 jaw independent, one 3 jaw that only has the standard jaws, one 3 jaw that only has the reversed jaws and soft jaws. If I did not have the chuck with the soft jaws already I would probably have bought a chuck that had soft jaws as an option. The option of buying new standard or reversed jaws for these old chucks is not available

I have a threaded spindle nose for which purchased back plates are not available so making my own is the only option. Had to make a faceplate to suit as well. This doubles up as a catchplate.

Guess I'm totally confused. I thought you posted it was an ML7 and five tailor-made backplates would cost 100 quid.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Hopper on 21/12/2016 08:46:43:

Guess I'm totally confused. I thought you posted it was an ML7 and five tailor-made backplates would cost 100 quid.

.

Check the authorship of the opening post.

MichaelG.

[MalcBParticipant @malcb52554]

When i was making backplates up to 160mm diameter for my last boxford I went to my local ferrous bar stockist and cast iron sawn blanks were actually about 25/30% more than buying steel ones. The price of blanks is not far from that of ready made ones.

I went to RDG and bought some 160 dia castings but they were literally very poor castings with large blow holes opening up as i was boring and screw cutting. Wasted quite a lot of time proofing rubbish material. Others may be lucky but i wasnt. Ended up using steel profiles.

I actually bought a couple of ready made ones and was quite pleased with the quality for the money.

My Conclusion:

If you can latch on to a source for decent quality ready made plates ( and there are probably more available for Myfords than any other ) then go for it as you have still plenty to do in fitting them. You will release more time for more importand or urgent projects.

If however you get a lot of pleasure from making your own workshop equipment and you are not chomping at the bit to get on with other stuff then make your own. Your financial saving is minimal though. Personally I would discount buying a tap and just finish screwcut them to size. I used single point for roughing the thread and finished to size with a well relieved and backed off internal chaser which gives good thread form. I actually remove all but the first two teeth.

Remember – Model Engineering/Home Workshop ( when not undertaking for financial gain) is about Enjoyment and learning. Ignore minimal financial differences and go for pleasure gain every time albeit making them thru' or buying ready made and moving on to next project.

[Andrew TinsleyParticipant @andrewtinsley63637]

I seem to have raised some interest as to why I want 5 backplates for an ML7 lathe. It is pretty simple, one 6" independent 4 jaw. Two 4" three jaw chucks (one precision Pratt Burnered for best and a tatty TOS one for rough stuff!). A three (soft) jaw chuck (invaluable when you need one!). Finally a Pratt Burnered six jaw precision chuck for delicate rings (mainly optical stuff).

The above collected over the years for the happy day when I could get started again!

Andrew.

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