Acme thread

This topic has 13 replies, 6 voices, and was last updated 23 August 2017 at 15:55 by Clive Foster.

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23 August 2017 at 07:59 #313487
Piero Franchi
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@pierofranchi37209
Hi There

Could do with a little help

I have around five spare lead and cross slide screws for a lathe I am trying to identify

now can you tell if either of them are metric or imperial ???
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23 August 2017 at 07:59 #25459
Piero Franchi
Participant
@pierofranchi37209
identifying
23 August 2017 at 08:16 #313491
Tony Pratt 1
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@tonypratt1
The outside diameter should give you a good indication.

Tony
23 August 2017 at 08:18 #313492
Piero Franchi
Participant
@pierofranchi37209
I am at home at the mo with only a steel rule, but it the one I am trying to identify does look closer to 15mm than any thing else.
23 August 2017 at 08:23 #313493
John Haine
Participant
@johnhaine32865
Measure the length of 10 or even better 20 pitches along the screw with your mm steel ruler, then divide by the number of pitches you counted. Do this 3 times and take the average, even better. Diameter is not a good guide, e.g. 5/8 inches will look like 16mm if all you have is a steel rule.
23 August 2017 at 08:27 #313495
Tony Pratt 1
Participant
@tonypratt1
Well could be 15mm or maybe 9/16", if you want to sell them you will need to confirm the exact diameter & thread pitch.

Tony
23 August 2017 at 08:30 #313497
Piero Franchi
Participant
@pierofranchi37209
The screw in question is a New old stock lead screw that came in a wax covering, it was in a Colchester light green hard plastic long bag (opened)

the part number on the Colchester plastic bag reads 2155

I am looking to make sure the lead screw does indeed match the part number
23 August 2017 at 08:55 #313502
Nick Taylor 2
Participant
@nicktaylor2
2155 would seem to point to it being a metric crossflide feedscrew for a Chipmaster, at least according to my manual. It should be complete with nut. If only it was imperial I would make you an offer!
23 August 2017 at 09:04 #313507
Piero Franchi
Participant
@pierofranchi37209
It is complete with nut,

I have two, one sealed in the wax and one opened

But for some reason, I am not 100% sure its for the chipmaster.

as I said, the wax sealed one came in a opened hard plastic cover/bag

there is nothing to say the bag is NOT right for the part.

I am trying to find a photo on google of one so I can compare it, but have had no luck

the colchester parts manual does not show the part very clearly not does it give details
23 August 2017 at 10:37 #313534
Piero Franchi
Participant
@pierofranchi37209
I have just up loaded three photos of the lathe screw to my profile photos in case any one knows what its from
23 August 2017 at 13:52 #313569
Bazyle
Participant
@bazyle
If your question is just whether it is metric or imperial you have at least 150mm there to get an accurate measure of the pitch. If the question is really whether it is for a chipmaster then you need to measure and list more of the key features as it is likely to be very similar to other models, Student, Triumph etc. Then probably go to a specialist forum like the Colchester yahoo group.
23 August 2017 at 14:51 #313584
Nick Taylor 2
Participant
@nicktaylor2
From your pictures the nut looks exactly like the type fitted to my Chipmaster. I have never removed the screw so can't be 100% but it certinatly appears to be a Chipmaster part

Edit – unfortunately the Colchester yahoo group has been dead for some time, I'm not sure where else to reccomend.

Edited By Nick Taylor 2 on 23/08/2017 14:52:06
23 August 2017 at 14:56 #313585
Piero Franchi
Participant
@pierofranchi37209
I was hoping ti identify it so I can find a home for it,

Its pointless me holding on to a New old stock lathe screw when I am sure there are people out there who would love to have and use this.

its no good for my lathe
23 August 2017 at 15:55 #313593
Clive Foster
Participant
@clivefoster55965
Many imperial TPI and metric pitch threads are closely equivalent sizes. Its relatively easy to get the approximate pitch or tpi in either system but telling the difference between an imperial thread and the closely similar metric one, or vice versa, is more difficult.

The trick is to calculate the length of thread giving a half pitch difference over a measured length between the two very similar candidates. This is easy to see with a ruler as that measurement doesn't need to be anything like precise. Typically you need to measure over a few inches, maybe 5 to 7, for half pitch error.

First time I did this was after buying a Bridgeport feed screw and nut set which didn't screw together and needed to figure out whether screw or nuts were wrong. I was able to verify that the 5 mm pitch Bridgeport feed screw I'd bought was in fact 5 tpi so the nuts were 5 mm as required. A tricky example as the two are close enough in size that worn nuts will go on the wrong screw in a fairly satisfactory manner.

I have a spreadsheet somewhere with all the common pitches and tpi mapped out besides the half pitch error lengths in both metric and imperial dimensions. Fortunately there aren't many variations of tpi or pitches in common use.

Clive
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