Colchester: How to determine if missing leadscrew is metric/imperial

crystalltiice · Sep 6, 2018

Hi,

I have the option to buy a colchester lathe with missing leadscrew and possibly also a missing half nut.

The machine was stripped for repairs and then some parts were stolen. Some gears from the apron might also be missing. How else can one determine what the leadscrew should be? It would be a rather expensive mistake getting the wrong one!

It is for a mascot/mastiff.

Also, would stock acme "threaded rod" of the correct pitch work as a cheaper alternative to an original part??

Thanks

john.k · Sep 6, 2018

Colchester will be able to tell you from the serial number......provided ,of course its not an antique "round top".........stock acme would have nowhere the accuracy of pitch needed for a leadscrew.......but a lathe ,especially a large one,isnt used for threading very much,so no leadscrew is no loss.

machtool · Sep 6, 2018

crystalltiice said:
Hi,
I have the option to buy a colchester lathe with missing leadscrew and possibly also a missing half nut.<br>

The machine was stripped for repairs and then some parts were stolen. Some gears from the apron might also be missing. How else can one determine what the leadscrew should be? It would be a rather expensive mistake getting the wrong one!<br>
It is for a mascot/mastiff.
Also, would stock acme "threaded rod" of the correct pitch work as a cheaper alternative to an original part??<br>

Thanks

Surely the dials are engraved with increments per turn. Something that does 6.00 mm will be different to 1/4" (6.35mm) What do the hand wheels tell you?
Hand wheels have to be a direct ratio of the screw pitch. No 127T gear required. Hopefully they weren't stolen as well.

Yeah Yeah technically the hand wheels work off rack and pinion. So has no relation to the lead screw. But its a Colchester, even they couldn't stuff that up. Interracial lead screws / feed racks Imperial v Metric

Regards Phil.

john.k · Sep 6, 2018

The reason I ask if its a roundtop,is that they had a fine pitch,three start leadscrew,and a half nut,one not two......consequently the leadscrew frequently was stuffed.....now the simple cure was to end for end it,and replace the half nut.......which was made of cast iron,malleable.In any case,the price of parts ,if available will be eye watering.

crystalltiice · Sep 6, 2018

I was thinking something like this: Alloy Steel Acme Threaded Rod | MSCDirect.com

The have a 2C fit which is "more precise", not sure how that compares with a factory colchester leadscrew. Any price is eye watering to me right now with the exchange rate!

How/where does one get hold of colchester to query about the serial number?

Here is another possible supplier: Keystone

john.k · Sep 6, 2018

Firstly....is it a roundtop or square/later ?....Secondly,a leadscrew of the wrong pitch isnt much good ,unless you have an old style changegear lathe.......Thirdly...why do you need a leadscrew?.......Fourthly,do the power feeds work?.....(before buying also be sure to have the lid off,and check for disasters in both head and feed gearbox.)......I realize that needs must when the devil drives....EDIT...Colchester is Harrison,dunno if they still make manual lathes,

machtool · Sep 6, 2018

crystalltiice said:
How / where does one get hold of colchester to query about the serial number?

Limy & Tyrone are far better placed than me. But the 600 group own the name now.

6 Group PLC - About Us - Company History

In the 1980s, the Group established a strong market presence in the US through the acquisition of Clausing Industrial and largely disposed of its original UK metal and general engineering businesses.

You could ring them, but you will largely speaking to a wanna be wanker that wasn't good enough to get on the Footsie

john.k · Sep 6, 2018

The 600 group was always the parent of Colchester,Harrison and Richmond.....Hiab Truck cranes too.I used to work for 600 Group in Brisbane,in the truck cranes.....even then the lathes was small peas,....stuck in a little office at the back.......I remember the salesman telling me Colchester were having a sellout of old parts,dirt cheap........NOT....the only thing even then was the colleges had Bantams and Student/Master......I remember the Qld Uni, bough a Magnum for the physics department.....never used ,Physics was ousted by Law Faculty,the Magnum went in the scrap.....too dangerous to sell to the public,said the risk assessor,and too costly to modify!

crystalltiice · Sep 6, 2018

This is the newer square headstock.

The apron was removed with the leadscrew, power feed shaft and also the square FWD/REV shaft. The place was burgled and the 3 shafts and some loose gears from the apron were stolen, or so the story goes.

Threading on the lathe will be needed hence the quest to repair. Will take a look at it closer to the weekend.

The acme rolled screws have a lead error of 0.008"/ft for the 2C but they also offer other grades, not sure of the tolerance on them and also not sure what the tolerance should be on a new colchester leadscrew.

john.k · Sep 6, 2018

Found Colchester ,no trouble.....spares are a bit rich...drill chuck and arbor..437 quid............i would say if gears are missing,you are going to need a parts machine...Even used parts are astronomically priced.See if you can find another machine to inspect....but they wont let you dismantle it!

gbent · Sep 6, 2018

If you are truly looking at importing acme screw stock from the US, look at Green Bay Manufacturing.

Green Bay Manufacturing

ripperj · Sep 6, 2018

It doesn’t sound like you need perfection if you are considering off the shelf rod. You could get someone with a lathe in nice shape to to make you one, probably be cheaper than the manufacturer, and most likely better than off the shelf stock

Sent from my iPhone using Tapatalk Pro

NAST555 · Sep 6, 2018

Have a look at Forest and Holmach fhmt.co.za It used to be the 600 group SA but they bought it over a few years ago.
They have the 600 group now over here but I suspect you might crap your pants when you get a quote. Where about are you?

Also I am hoping that you just put the link to a US site for an acme screw as an example?

NAST555 · Sep 6, 2018

Oh and I have a few colchester students here and a baby Spartan. Probably also a few spare change gears if you need.

crystalltiice · Sep 7, 2018

Thanks for the replies guys.

I think I found a way to determine metric/imperial leadscrew: the gears on the swing arm are different for each. I found a triumph 2000 manual and I would assume that other colchesters will have the same ratios of gears for these parts if the leadscrew pitch is the same. So I will use this info to try and identify the leadscrew and go from there.

There was a discussion on another forum regarding the precision required for the leadscrew and as someone pointed out, one will rarely cut a very long thread that would require the lead error to be that accurate.

I have not sat down and done much thinking about this but if it is like a dividing head where the errors on the plate are divided by 40 then the lead accuracy of the leadscrew might not be that critical.

Getting the leadscrew made locally is something I considered but the only friend I have with a lathe big enough refuses to do it or let me use his machine to do it, he has made screws in the past and based on this has decide not to do it anymore. Paying normal rates for another company to do a one off might be much more expensive than a imported "mass produced" rolled one. Will have to phone around and see.

In the end I might just have to phone the 600 group and find out from them but legend goes that they got their name because all their prices are 600 times more than what you would expect to pay!

thermite · Sep 7, 2018

crystalltiice said:
Threading on the lathe will be needed

Restart your search, then. You were looking for a lathe when you found this one.

Find another lathe without the problem. By this stage, you should be aware it is none of fast, simple, nor cheap to sort this one. And you haven't YET twigged to what ELSE might need costly parts, nor all the reasons these ones were removed in the first place.

Not a positive signal.

A less problematic lathe should come out cheaper in the long run, if not also "right away". Don't "fixate" on this one machine. LOTS of folks have uses for a lathe that will never even ONCE call for them to single-point a thread on it

NAST555 · Sep 7, 2018

Exactly which Mascot/Mastiff is it? Swing/between centres/spindle bore? Have a pic?
You never know, there might be a guy on this forum that sees a hell of a lot used machinery go through his shop, has lots of contacts in the industry and is willing to help if he knew where you are based. Hell, he might even be from the same country as you!

thermite · Sep 7, 2018

NAST555 said:
Exactly which Mascot/Mastiff is it? Swing/between centres/spindle bore? Have a pic?
You never know, there might be a guy on this forum that sees a hell of a lot used machinery go through his shop, has lots of contacts in the industry and is willing to help if he knew where you are based. Hell, he might even be from the same country as you!

LOL! Keerful, there. Not TOO close!

Next thing yah know he might even wonder if it's the same one as "burgled" the missing parts!

RC99 · Sep 7, 2018

What you could do is the native leadscrew pitch will be 1:1 ratio with the spindle.

So put the threading pitch at 4tpi and if the leadscrew shaft rotates exactly once when the spindle rotates exactly once, then the leadscrew was 4tpi, it could also be 6mm or 2tpi or 12mm.

If the original leadscrew was 6mm and you set it at 4tpi, then the spindle to leadscrew ratio is not going to be 1:1. as 1/4" is 6.35mm. (from memory)

crystalltiice · Sep 7, 2018

Yeah, like the guy who found his stolen car something like 19 years later on a property he visited!

Will go and look at the lathe on the weekend. Not really fixated on it but if I can get it for a bargain and fix it up for not too much then it is worth it. But yes, I own too many money pits already!

Colchester: How to determine if missing leadscrew is metric/imperial

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