MagXact scale install....chasing my tail on tolerances.

[Beantown]

After months of sitting, I'm finally getting a chance to get my new lathe and mill setup. However, I'm chasing my tail trying to hit the tolerances of 0.1mm (0.004") with mounting my magnetic scales on my PM-1440GT. I can hit 0.002" one way, but then when I try to adjust the other it blows the first out out.....by a lot. Maybe I'm crazy, but it's that tolerance a bit extreme? For one, the castings on my lathe is rougher than a petrified log. Second, the included mounting blocks have more than a 0.004" variation in the coating. Third, I'm measuring on the scale itself that flexes and it's extruded aluminum...again with a variation of more than 0.004".

What am I doing wrong here? It's pretty frustrating how awful the instructions are that came with the kit from Precision Matthews. They are about on par with something you could get with a Wish.com item. At this point, I'm not impressed with anything from PM. Not sure what I'm paying for with them. They wouldn't even send me a picture of how they install them on their own machines.

 

[coolidge]

I think the .1mm per meter (.004 inch) per meter spec is a bit extreme. You don't want to seriously bend or twist the scale but you have a whopping .027 inch tolerance between the read head and the scale, plus more for the read head not even being parallel.

On my last lathe I mounted the Z axis scale onto a long piece of THICK aluminum flat bar then mounted the flat bar onto the lathe with some grub screws for adjustment. Way easier because the aluminum magnetic scales quite easily twist and bend. Trying to adjust the scale on its own without the aluminum flat bar was maddening. Between the lathes thick paint and hidden spots of bondo the little provided grub screws can't deal with it.

 

[coolidge]

By the way I'm getting ready to install this same MagXact DRO on my new 1440 lathe. Already got my aluminum flat bar for the Z scale, 3x.5 inch.

 

[Beantown]

Thanks for the reply. I originally planned to do something similar to your suggestion, but there are some weird stickouts that look like they are for mounting a scale in the way. Unfortunately they don't come close to aligning. If I can't get this done today, I will probably revert back to that plan. I can mount some 5/8 bar to the stickouts and then get that all precise and then mount the scale to that.

I can get my mounting points in all directions to within 0.002, but between the center block and the end blocks I'm getting about a 0.04 bow no matter what I do. I'll keep fiddling with it and try the grubs on the scale itself.

 

[coolidge]

Bowing, twisting is exactly why I went with the alum flat bar approach. The scales are not exactly a wet noodle but at those lengths on Z they have very little resistance to bowing and twisting.

LMAO this is bringing back memories of me cussing and throwing **** before going with the flat bar method.

 

[Beantown]

LMAO this is bringing back memories of me cussing and throwing **** before going with the flat bar method.

LOL Thank you for saying that. I get frustrated when things don't go as I think they should, so it's refreshing to know I'm not the only person that has the occasional tantrum in their shop. I think I'll just set this project aside until I can get the aluminum tomorrow. Otherwise, I'm going to have a bad day.

Since you have the same kit, where you shocked by how generic it was? Did you get more than a one page manual that was folded into four squares? I made the assumption that using the kit from PM would be easier than from someone else. After getting this one, I'm 90% sure the DR PRO kit would have been easier to install.

 

[woodchucker]

sorry, too busy to read through this thread right now. in the middle of some glue ups.
assuming the tolerance is front to back, use jack screws to create your level... just install set screws below the face of the blocks, and adjust, tighten your hold down screw and voila.

 

[mksj]

Magnetic scales have a wide tolerance for misalignment vs. glass scales, example below. One magnetic scale that I installed I originally had a 0.2" gap and still worked until I did some adjustments to the bracket. Seems like you are applying glass scale tolerance to your magnetic scales, which is not necessary.

 

[Beantown]

Magnetic scales have a wide tolerance for misalignment vs. glass scales, example below. One magnetic scale that I installed I originally had a 0.2" gap and still worked until I did some adjustments to the bracket. Seems like you are applying glass scale tolerance to your magnetic scales, which is not necessary.
View attachment 501738
View attachment 501736

Interesting! My instructions look just like the top image you posted. I wasn't sure was the EMRA,B,D meant....My scale has a 2.0MM written on it, so I was guessing it was the resolution or something? In that case my tolerance is. 0.5mm which was more than I was allowing myself. Nevertheless, I still wasn't able to get that close.

 

[Beantown]

sorry, too busy to read through this thread right now. in the middle of some glue ups.
assuming the tolerance is front to back, use jack screws to create your level... just install set screws below the face of the blocks, and adjust, tighten your hold down screw and voila.

Yea, that is what I did, but I'm getting a weird bow between the blocks that I just can't get out. I can get everything good at the mounting points, but between blocks is a corkscrew.