Possible Purchase of PM-25MV

[devils4ever]

I found that I actually have a Lenovo ThinkCentre M92p with 240 GB SSD and 16 GB of memory. It's a very small "desktop" PC.

I installed LinuxCNC 2.7.14 on it. I'm running latency-test now, but I'm thinking that the numbers don't really matter if I plan on using a Ethernet motion controller. Correct?

I'm trying to figure out the differences between the Mesa 7I96 and the 7I76 besides the $80 difference in price!

 

[rsnpt]

View attachment 304857

Be sure to carefully align the X axis lead screw before tightening down the nut bolts, it's too bad there is no way to access it when the table is mounted.

Hi guys,

I recently bought a milling machine and decided to take it apart to clean and get to know it a little better. Handfuls of casting sand removed...

Now that everything is clean and reassembled in modules I'm putting it together.
I removed the X axis brass nut and now I'm having a little trouble aligning it correctly as when I fit the table and both doweled ends I have to force the screw to bend a little. Obviously I don't want to make that happen, so, what is the correct way of aligning this nut?

I had no issues with the Y and Z axis nuts but this is getting very time consuming as the whole table must be removed in order to access the nut. I need to find out the proper way of aligning it. Help?

Thanks

 

[codexmas]

Hi guys,

I recently bought a milling machine and decided to take it apart to clean and get to know it a little better. Handfuls of casting sand removed...

Now that everything is clean and reassembled in modules I'm putting it together.
I removed the X axis brass nut and now I'm having a little trouble aligning it correctly as when I fit the table and both doweled ends I have to force the screw to bend a little. Obviously I don't want to make that happen, so, what is the correct way of aligning this nut?

I had no issues with the Y and Z axis nuts but this is getting very time consuming as the whole table must be removed in order to access the nut. I need to find out the proper way of aligning it. Help?

Thanks

I just moved and reassembled my mill for the second time. The x axis screw alignment was off a bit, there was a variance in the force required to move it. I was considering a few different options on how to diagnose it without removing the table again, but gave in and took it off. It really doesn't take much time after you have done it once or twice.

I found a piece of aluminum profile that I could rest along the back dovetail and then eyeball the very ends of the screw to see how well aligned it was.
The rear dovetail is parallel to the screw, the one at the front is pretty obviously tapered, which is how the tapered gib does it's job. So the front one is not a good reference for how parallel the lead screw is.

So, it sounds like a lot of work but you will be happy you did it, even if it takes a few tries. Take the table off, find something to use as a reference to align the lead screw. Rinse and repeat. You will very easily be able to tell when you have gotten it right.

There is no documentation on this process that I could ever find, it's left to the owner to get to know the machine and the feel for it.

 

[rsnpt]

Thanks for your reply. I tried your method and it worked well as long as the table was centered, but when I moved it to both ends it was getting harder and harder to turn the handles. Eventually I found out the lead screw was OK when the table was centered but was very offset when the table was pushed to one side.

I only had one of the bearing housing ends removed, so after removing the other I was able to slide the table without actually removing it.
I ended up just setting the nut in place with the bolts slightly free, mounted the table and both ends, moved the table to adjust the nut to where it wants to be and then disassembling everything very carefully to not move the nut. Then torqued it and on reassembly all was good again, very smooth end to end. That's one sorted.

Now my next issue is tramming the head. I'm not sure where my issue is but I have 0.002" over 6 inches on the Y axis.

I'll describe what I did (not sure if the digital DTIs are the best tools for this, but they are what I have at the moment):

- mounted the column and checked it on the X axis. This:

- locked X and Y axis
- with one of those T shaped tools with a DTI on each end (6 inches) adjusted the Y axis and found out I had 2 thou difference on each end (lower value at the column end).

Trying to figure out if the issue is the head or column:

- I set up a known good square (200mm) on the table and checked it vertically with the DTI, base attached to the Z axis saddle. I was not getting consistent results as the values were changing as I cranked the handle.
- Then I set up another DTI on the spindle running against the opposite edge of the square. With this I noticed that when I changed the direction of movement (up/down), the Z-axis side DTI was showing 0.0015-0.002" of movement while the spindle DTI had no movement. Also, running down the square edge, I had more movement on the Z-axis side than the spindle side. Video here:

- I checked and re-checked the gib and I believe it is actually too tight, but it does run much smoother in the middle than on the top 1/3 of the column.
- Using the T tool with the DTIs I set the head on the X axis (easy) and re-checked the Y... again 2 thou.
- With the DTI held on the side of the head I run it on the table in the Y-axis, end to end, 0.0005" difference, so I believe my table is not tilting (I don't have a precision level yet).

What do you think of this? What could be tested next to find out where the problem is? I'm not understanding where I should be shimming it, or if I should at all.

One thing I noticed is that I can push the head and measure the column flexing, maybe 3-4 thou. I think the head really pushes the column forward and makes the setting of the Y axis really difficult. Do you guys notice the same?

Also, when I run the DTI on the spindle by lowering the quill (running down on the square), z-axis locked, I see around 8 thou at the end of the travel. It starts slowly with 2 thou and then right at the end... 8 thou. Do you guys see the same on your machines?

I'm sorry for so many questions, I'm just a newbie trying to figure out my new machine.

Thanks

 

[codexmas]

I would start with the simplest tramming operation first, an indicator mounted on a bar that is chucked in a collet in the spindle.
The bar length doesn't need to be more than 4-6 inches really, getting within a thou or so over 8-12 inches for machines this size is really as good as you can expect.
Even if you went for a longer bar, swinging it from left to right over a longer distance these mills are known to go out on their own after a while.

Nod is something you would have to shim out, or use epoxy to lift the column, each their own issues. Shims make the whole column less rigid and epoxy is going to be a mess to deal with and a lot of trial and error getting it to the right level that you want.

I also started out with the newbie "chasing the numbers" syndrome, and now just work with it instead. Getting to know how much those values matter, or not, is a whole lot more useful than dialing it all in only to see it shift again.

Get it close, start making chips and get to know the machine, what you can do with it and then start tweaking when it starts to matter.

Just my thoughts on the subject, we all have different goals, mine is just a hobby with very sporadic use.