My new CNC toy

Thread Starter

spinnaker

Joined Oct 29, 2009
7,830
I agree with @cmartinez they do have the Appearance of ACME screw.;)
I wonder if they sell a bare bones machine, no electronics/motors?
Max.
I have seen a 6040 on eBay sort of bare bones. Could not remember if it hadhad motors or not. But for sure no controller. You guys are dissing it but I think it is a great deal for what you get and lets you dabble in cnc without a huge cash outlay.
 

jpanhalt

Joined Jan 18, 2008
11,087
No, ACME = A.C.M.E. It is an acronym. There is a small difference between ACME threads and metric ISO trapezoidal threads (29° vs. 30° included angle). The ACME thread is a little stronger and can be metric by actual dimension, I think.. When I mentioned it, I used ACME to equal any trapezoidal thread. The Chinese are known to use many unusual threads. Not all are metric. I even have an HF horizontal/vertical bandsaw with Whitworth threads!

John

Edit: What I meant, if it wasn't clear from context, was that that thread is not a ball screw thread. At least, I have never seen one like that, including even imprecise rolled ballscrews. Ballscrews are popular solutions to backlash, they do not necessarily provide better accuracy.
 
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GopherT

Joined Nov 23, 2012
8,009
No, ACME = A.C.M.E. It is an acronym. There is a small difference between ACME threads and metric ISO trapezoidal threads (29° vs. 30° included angle). The ACME thread is a little stronger and can be metric by actual dimension, I think.. When I mentioned it, I used ACME to equal any trapezoidal thread. The Chinese are known to use many unusual threads. Not all are metric. I even have an HF horizontal/vertical bandsaw with Whitworth threads!

John
Threads of all types can be found in Asia. Especially difficult are the mix of threads (imperial, metric and other), couplings and flanges for pipe. Especial troublesome since some of the flair fittings nicely fit into other types of threaded pipes - without making a seal.
 

cmartinez

Joined Jan 17, 2007
8,250
I agree. Compression fittings are particularly troublesome. You can't tell the differences by eye.

John
Just look at the subtle differences between american and british threads for that sort of fitting... one could easily face a nightmare scenario if they were to be confused when working with liquid propane, for instance.
 

Thread Starter

spinnaker

Joined Oct 29, 2009
7,830
My first engraving attempt. Not exactly a success. :) For some reason coming out mirrored. Need to contact the author of the engraving software.


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MaxHeadRoom

Joined Jul 18, 2013
28,669
@ cmartinez and maxheadroom, threads are in all probability metric. That makes the a trapezoidal thread not acme.
In this case the comparison amounts to the same thing, a ballscrew 'groove' is shaped to take the radius of the recirculating ball nut(s).
IOW not a square shouldered thread.
There are basically two types, the superior precision ground type and rolled ballscrew type.
The advantage to a pre-loaded ballscrew is zero backlash.

Max.
 
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cmartinez

Joined Jan 17, 2007
8,250
The advantage to a pre-loaded ballscrew is zero backlash
And then there is the double pre-loaded ball screw (which also applies to acme and trapezoidal) in which two nuts (ball or acme/trapezoidal) are pushing against each other separated by a spring. It's far cheaper than a true pre-loaded ground ball screw/nut.


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shortbus

Joined Sep 30, 2009
10,045
And to further muddy the waters - I'd be willing to bet that the threads are at least double start. Any machine I've ever been around that was built originally as a CNC (not converted to CNC) has a two or sometimes three or more start thread. A CNC Bridgeport mill is a double start 0.400" pitch, 0.200 lead screw in it. Even the trapezoidal threads lead screws sold for small engravers like this are usually double start.

Many of the precision ball screws are rolled now days. And the backlash on them is controlled by the fact that the are multiple start, not the precision of the cutting/rolling of the threads. The precision is the tolerance of the pitch over a given distance.
 

Thread Starter

spinnaker

Joined Oct 29, 2009
7,830
Well it took a lot of messing with linuxcnc, lots of adjustments on the new machine, lots of investigating of various gcode isolation layer wizards, lots of messing with depth and width settings. But I think I finally got it! Almost gave up on trying to figure this all out. I might try to write a blog once I get all of my thoughts together.

It is so cool to watch that little machine moving around. The fact I will no longer need to drill will be worth the price of the mill. I do find the drilling the PCBs a bit therapeutic but it is a long process for me. I can only drill 6-10 holes at a sitting or I start missing the target or breaking bits. It will be nice to have the machine do the dirty work for me. :)


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