View Full Version : ACME / Trapezoidal leadscrews

26-02-2009, 02:01 AM
Yet another question in my bid to gain knowledge :).

Does anyone know the metric trapezoidal equivalent to various ACME leadscrews?

ACME leadscrews are sized as say 10tpi single start, so 10 rotations = 1 inch of travel. A 10tpi 2-start has 5 rotations = 1 inch of travel, in metric land the 10 tpi single start is equivalent to a 2.54mm pitch trapezoidal leadscrew I believe, but what is the equivalent to the 10tpi 2-start? 5.08mm 2-start?

This is almost frustrating, I started out thinking 'I want to do ZXY', but every time I look at any particular part it throws up more and more questions :eek:. Fortunately I love meeting challenges, and solving problems so this is still fascinating & fun :D.

Just to give some idea of what I'm thinking, my plan is something like this:
I want to build a basic router as a learning exercise, that I can then use to make the (first :D) proper router with. I am thinking of the proper router being something similar to the Joe's 2006 R-2, and to save money I want to build the basic one using parts that can be reused, i.e. x-axis leadscrews and bearings of the basic becoming the y-axis of the Joe's 2006.

If you think I'm completely mad let me know :D I already know I'm slightly mad ;).

Or if you've got any suggestions for different machines, parts, or anything really, please speak up :).

BTW the reason for the original question in this post was that alot of people in the states are using 10tpi 2-start, or 8tpi 2-start ACME rods with success in their Joe's 2006 routers, and I don't want to blow 30+VAT and delivery on the wrong material...

John S
26-02-2009, 09:22 AM
basic rule of thumb is Acme is usually imperial, trapezoid is usually metric so you get 1/2" acme versus 12mm trapezoid, also often know as power screw over here.

Acme is usually a cut thread and trapezoid is usually a rolled thread.

Another thing to bear in mind is that 10 tpi two start is worked out as 5 tpi, the greater the tpi the more torque you need to move a carriage.

Good website here.


John S.

26-02-2009, 05:36 PM
Thanks John, had a look at that web site, and it didn't clear the fog from my brain :confused:, but then I found http://www.automationcomponents.co.uk/ things are making sense now :).

As I understand it (using Marchant Dice codes as an example) a TR16-8P4 screw is 16mm in diameter, would move 8mm per revolution, and has 4 starts. Anyone able to confirm this for me?

Also MD don't seem to sell multistart nuts at all?! seems a bit strange.

26-02-2009, 09:27 PM
Another thing to bear in mind is that 10 tpi two start is worked out as 5 tpi, the greater the tpi the more torque you need to move a carriage.

Don't you mean the lower the tpi the more torque? I don't need help with being confused ;). Ignoring efficency issues 5 turns per inch of travel has to take more torque than 10 turns per inch.

John S
27-02-2009, 12:20 AM
Just testing to see if you are awake...............:D

John S.

22-03-2009, 05:58 AM
did u happen to find any acme 5/8 5(2) nuts [ie 5/8 diameter, 10TPI and 2 starts]
so far i only see stuff at roton , around $25 or more per nut...

25-03-2009, 10:23 AM
Sorry, not been around for a bit.

I've had to stop plans for my router for a while due to job issues :( so I've not been looking, I had pretty much decided to go with delrin drive nuts, and make them myself by using a section of leadscrew to make a tap for the threads.