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leadscrew pitch

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David Keil 109/02/2021 18:20:47
24 forum posts
7 photos

as a newbie to a milling machine, I am trying to find out what this means in relation to a leadscrew pitch, 6.3 x 1mm.

JasonB09/02/2021 18:29:48
20880 forum posts
2318 photos
1 articles

That's a bit of an odd one can you give us a few more details of the machine and the context of the text.

Pete Rimmer09/02/2021 18:30:24
1004 forum posts
57 photos

The pitch is 1mm David.

David Keil 109/02/2021 18:35:20
24 forum posts
7 photos

The machine is (or will be) a Sherline milling machine. I am going to use mach3 so just trying to understand how to setup motor tuning in mach3.

David Keil 109/02/2021 18:36:17
24 forum posts
7 photos


what does the 6.3 relate to?

Emgee09/02/2021 18:54:19
2105 forum posts
264 photos

6.3 (mm?) could be the 1 decimal place American conversion of 1/4" diameter feedscrew.


Edited By Emgee on 09/02/2021 18:55:28

Howard Lewis09/02/2021 18:55:47
5036 forum posts
13 photos

6.3 mm sounds like a slightly inaccurate 1/4" (6.354 mm )

Don't know the Sherline, but imagine it as a fairly small machine, so could the leadscrew be 1/4 x 25 tpi?

Hard to imagine that a designer would specify a 1 mm pitch for an odd diameter such as 6.3 mm..

It could be hybrid with a 1 mm pitch on a 1/4" shaft.

Having been told that the by Pete Rimmer that the pitch is 1 mm, I would expect the diameter to be a Metric integer.,

The essential thing is that the OP KNOWS the pitch so that he write the program


SillyOldDuffer09/02/2021 19:02:04
7341 forum posts
1617 photos

I guess this comes from Sherline's Specifications Page. 6.3mm is the diameter of their metric leadscrew.

Sherline's Inch leadscrew is given as ¼ - 20, which is USA speak for ¼" diameter rod threaded 20 turns per inch.

The metric leadscrew is given as 6.3mm x 1.0 pitch, which is similar in size to the inch version, but the dials measure in metric.

6.3mm x 1.0 is a non-standard metric size. I think for ease of manufacture Sherline have just put a metric 1.0 pitch thread on the same ¼" diameter rod they make ¼ - 20 from. Quarter of an inch is 6.28mm, close enough to 6.3mm.

For setting up CNC only the pitch matters - the 6.3 can be ignored.


Edited By SillyOldDuffer on 09/02/2021 19:04:06

Michael Gilligan09/02/2021 19:02:44
18325 forum posts
872 photos

Here it is, straight from the Sherline horse’s mouth: **LINK**

I’ve never measured one [and there is no tolerance quoted] but can only assume that 6.3 is the diameter in millimetres

... either a truncated approximation for 6.35 mm, or because they actually skim down 1/4”



Dave beat me to the post.

Edited By Michael Gilligan on 09/02/2021 19:05:06

David Keil 109/02/2021 19:03:44
24 forum posts
7 photos

The 6.3 x 1mm is the sherline specification for the x and y leadscrew axis.

David Keil 109/02/2021 19:05:00
24 forum posts
7 photos

OOps you both beat me to it.

David Keil 109/02/2021 19:07:02
24 forum posts
7 photos

Thanks all for your help, so simple really....haha

Andrew Johnston09/02/2021 19:20:50
6129 forum posts
674 photos
Posted by SillyOldDuffer on 09/02/2021 19:02:04:

Quarter of an inch is 6.28mm, close enough to 6.3mm.

Last time I checked 1/4" = 6.35mm - exactly.

In case SoD thinks I'm getting at him again, he's not the only offender who doesn't know the equivalent of 1/4" in metric, just the simplest to quote.


DC31k09/02/2021 19:21:44
506 forum posts
1 photos

We have had long and interminable discussion in another thread about various definitions of the inch.

This here thread would seem to provide two more candidates:

the Howard inch, where 1/4 of it is equal to 6.354mm and the Duffer inch where 1/4 of it is 6.28mm.

Steviegtr09/02/2021 19:32:58
2141 forum posts
299 photos

So i guess & Howard & Duffer inch is somewhere in between.()


JasonB09/02/2021 19:44:18
20880 forum posts
2318 photos
1 articles

Would that be the "Howduff" inch?

Not to be confused with the typo inch.

Edited By JasonB on 09/02/2021 19:44:59

Clive Foster09/02/2021 20:18:27
2735 forum posts
100 photos

Feedscrews of metric pitch but imperial diameter has been very common on metric versions of machines originally designed for markets using the imperial system.

Which can be a right pain.

Telling the difference between 5 tpi and 5 mm pitch on Bridgeport feedscrews or nuts is hard enough when everything is new and factory fresh. Throw in a quater of a century of wear and its time to invent new swear words. Screws aren't too bad when you know the cunning trick to make it easy but nuts .....

Many years a go I chose the best fit pair from several loose cross slide feedscrews and nuts when doing a "frankenlathe" Boxford saddle on southbend apron and bed job. I know some were metric, some imperial and all were worn. I'm pretty certain that best fit pair was one imperial and one metric but which was which I know not. Worked just fine for me over a decade or so and the guy who bought it was happy.


Grindstone Cowboy09/02/2021 21:21:18
642 forum posts
58 photos
Posted by JasonB on 09/02/2021 19:44:18:

Would that be the "Howduff" inch?

The "Duffard", I think. smiley


David Marks 209/02/2021 21:45:14
16 forum posts

1/4 - 20 is a 1/4" UNC thread. A standard thread in the UNC/UNF series and the American equivalent to our BSW/BSF system of threads.

Oily Rag09/02/2021 22:55:57
434 forum posts
147 photos

Some years ago I was passing through Hong Kong on my way home from China mainland, the connecting flight 'missed' so I had 48 hours in HK before I could get another flight. In this time I decided to have a made to measure suit which would be ready in just 36 hours!

When I was being measured up I was surprised to discover that I had miraculously lost weight - my waist size had dropped from 34" to 27", my chest from 42" to 34"! That was when I discovered the Chinese tailors inch where 1 CTI = 1.25 Imp inch!!


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