Another PM940-CNC-VS Thread...

[phazertwo]

If your only interested in pics/tech/the good stuff… skip this next paragraph, trust me, I’d do the same thing. Also you will find a thread index at the end of this post, it should be useful for navigating to what you want to see and skipping all the BS

I’m FINALLY getting around to making a upgrade thread on my PM-940-CNC-VS, but first a little background. I have been interesting in fabricating ever since I realized a drill bit could cut metal, not just wood. Just out of high school I got a job as an apprentice machinist working for a crazy SOB, but I got plenty of hands on experience learning the ins and outs of, as some would call it, a “clapped out old Bridgeport milling machine” and some junky Chinese lathe. Later I was working for a different company where we had access to a small prototype machine shop, with a much nicer Bridgeport and a much nicer Cincinnati lathe. My interest in manual machining peaked during this time, after I made a few parts for my Toyota Pickup, which was modified for rock crawling. While working this job I was introduced to CNC machining via a vendor I became friends with… Fast forward years, and years, and actually over a decade later and 3 more jobs where I was always on the edge of learning CNC and I finally decided to take the plunge and buy a 3 axis bench top unit.

I had been thinking hard about buying a CNC, and of course dreamed of owning my own Tormach 1100, but not only am I not rich, I tend to be pretty cheap. So when I stumbled across the PM-940-CNC-VS (from here on out will call it the PM-940) I suddenly felt like I could actually own my own machine… That was in Januaryish of 2017 and the mill was in my garage setup and running by February…

Loaded on the trailer.

Wanted to put it in the truck as it would have been a smoother ride, but no way to get it out of something that high at home.

Didn't take any pics of unloading it. I had 3 buddies waiting for me when I got home and we made it happen in about 30min. It's current home:

Inside the cabinet:

I got a clamp set and a vise with the mill (forgot to take pics), turns out that the vice I ordered was out of stock, so they upgraded me for free BOO YA!

I do have to say, Precision Mathews has been an absolutely awesome vendor to work with. Questions answered extremely fast, all my pesky little OCD questions answered (like 20 emails worth)! I HIGHLY SUGGEST them. Keep in mind that I have had this mill for over a year before I even considered starting this thread and I still say that. The mill was completely functional out of the box, all upgrades that I’ve made or are making are because I’m serious tinkerer and I have a passion for precision/accuracy.

Anway, this thread will follow my adventures of upgrading this machine to hopefully be a bad-mamba-jamba that can keep up with a Tormach 1100, but for less money and with me learning a great deal more about CNC!

Here are two similar (like SUPER similar) threads that I follow, and that have inspired me:

cut2cut:
https://www.hobby-machinist.com/threads/my-pm-940-cnc-modifications.57976/

pburgh:
https://www.hobby-machinist.com/thr...ontroller-conversion-to-centroid-acorn.65196/

More to come!
PZ

Thread Index:

• First Chips - PG 1
• Ditching the nMotion
• Acorn Upgrade
• NC vs NO E-stop
• First chips with Acorn
• First metal chips
• Removing Z manual crank and gears
• Mist coolant
• Aluminum fixture plate
• First steel part

 

[phazertwo]

Right out of the box I was impressed with the quality of the machine. Everything was smooth, and short of some flaking paint was in good order. I promptly loaded Mach 3 on a computer and started setting up the machine. At the time I was eyeballs deep in a engine swap for my Toyota and desperately needed some custom fuel line clamps, so I designed them based on a piece of UHMW I had laying around and started programming. This was the first real part that I ran, and I ran 5 at a time, with profiling since I didn’t have the correct size ball end mill. I was ecstatic. I worked under the truck the whole time the machine was running and just listened for it to stop, at which point I would change tools and set it back in motion.

One of the finished parts:

At this point I was all smiles!

PZ

 

[phazertwo]

The honey moon didn't last long though. I had some issues that probably could have been resolved, like getting the limits to work right (which could have actually been loose wiring), the machine being very "jerky" and last but most importantly, I couldn't get the e-stop to be an e-stop. I would hit the e-stop and good two seconds would co buy before the machine would actually start to decelerate. After messing up a corner of my pretty vice and trashing two test parts and some mills when the machine didn't stop on time, I had had it. The nMotion and M3 were just not cutting it. So I started doing research on better controllers, you can read about some of the options and the decision I ended up making here, on page 2-3 of cut2cut's thread:
https://www.hobby-machinist.com/threads/my-pm-940-cnc-modifications.57976/

The Centroid Acorn was at introductory pricing at the very end of 2017, so I ponied up and made it happen!

While I was waiting on it to ship... This happened:

Never again would a lack of e-stop destroy a part, tool, or vice.

PZ

 

[phazertwo]

ACORN!

When I went to install the acorn, I realized that the back plane in the cabinet was setup for 3 or 4 drives, which makes sense because PM offers a 4th axis. So first things first was to move all the drives over to make some extra room.
Before moving the drives:

After moving the drives and with the Acorn in it's final resting place:

I used a simple piece of 1x2x11ga rectangular tubing and the original mount for the nMotion to mount the Acorn. It’s not the prettiest thing I have ever made, but it works quite nice.

The Acorn does not rob 5v from the computer, so a 5v power supply is needed. I used this cheapo mean well from amazon, seems to do the trick just fine. It mounted quite nicely behind the Acorn. I should have enough from for a 4th axis drive if I ever get one.

One thing I did that was against the recommendation of Centroid, but has caused no issues so far, is a shielded bulkhead connector for the ethernet cable. I would have liked to send it out the bottom, to keep crap from falling in it, but I didn’t have enough cable to pull it off, so its sticking out the top.

The specs for the computer to run the Centroid software is well above M3, so a new computer was in order. I was able to order components to upgrade mine for about $350. Hind sight being 20/20, I converted my dads router to Acorn as well and was able to buy a computer for $100 that worked perfect. Anyway, I shoved the computer back in the same cabinet near the mill.

Here is a list of the parts I used:

Meanwell 5v power supply

Shielded ethernet bulkhead connector

Shielded ethernet cable

PZ

 

[phazertwo]

Wiring the Acorn is a pretty simple thing. I think I re-used all the wiring from the nMotion, however you do need to add the 5v power supply. Acorn provides great schematics specifically tailored to different drives, so I just picked the Leadshine schematic and went for it. I didn’t make any changes to the VFD wiring or settings, just simply tied it into the analog output terminal of the Acorn and it worked flawlessly.


With the nMotion I could never really get my limits to work, and they needed to be switched form NO to NC. So I tore into that next, and it turns out that there were a few broken wires, and most of the terminals were loose. So I went through the entire machine and found that a fair number of the wires were loose. I would suggest to anyone who has a 940 CNC to check all your terminal connections to make sure they’re gooten-tight. After that the limits started behaving correctly.

This is how the limits need to be wires for Acorn:

Last thing had to do was change the settings in the Acorn to work with the normally open (NO) e-stop. An NO e-stop is quite dangerous, so I ordered up a new e-stop from the goold ol’ amazon and swapped it out two days later. All the wiring in the PM was quite nice, the loose connections could easily be from transport from China. The ONLY thing that I really didn’t like was the NO e-stop. I’ve been witness to a pretty bad industrial accident, and several smaller ones… don’t mess with e-stops and safeties. They are normally closed (NC) for a good reason.


After all the wiring was complete the Acorn fired right to life and connected to CNC12 no problem. I was up and running!

Parts used:
New E-stop

PZ

 

[phazertwo]

And I apologize, I didn't realize there was a time limit on editing posts... so the thread index in post one is dead. Unless there is a super nice/awesome/cool Mod out there that can either bestow upon me the access to keep editing, or just toss some links in there to keep up!

PZ

 

[phazertwo]

The Acorn was very easy to setup and tune. It still took me a night of dinking with it, but after setting up and tuning M3 it was no big deal. I wouldn't say it easier or harder, just different.

After all the tuning was done it was time to make some chips. I found myself at a loss of what to build, so I just made a gizmo in Fusion and had at it. I had some blocks of UHMW laying around, which I hate machining, but I figured what the hell, good for a test. I used all brand new HSS tools, so it worked out okay, but not perfect.

I ran most of it with a 4 flute 0.5" end mill at 3200 RPM and about 0.004 IPT with a 0.35" step over. It was a little nerve racking to watch this setup that I had done nothing but basic tests on run at 51IPM just chewing thru material.... Worked perfect, no hick-ups.

So I made a mating part, they fit super tight...

With just this one run under my belt, my confidenice was already higher than it ever was with the nMotion and M3!

PZ

 

[phazertwo]

After the plastic went so well, I setup to make and aluminum test part. I was worried about speeds and feeds for this, so I kept it simple. Just grabbed a scarp block of aluminum, faced it and put a slot in it.

Worked out perfect, and I was pretty happy with the surface finish of the walls of the slot. Next I flipped the block over and made something more complicated. Something that had some different features I could measure, and push my S&F's a little bit further.

Everything seemed to come out with in 0.002" or so, I'm thinking I measured the end mill wrong. It was the first time I programmed the fly cutter and it did great.... Except I didn't deck the scrap far enough, you can still see a little bit of the slot that was running through the center of it. This was also the first time I used the chamfer tool to deburr the part, if you haven't tried this I strongly suggest it, I do it on every part now. All and all for a test part I was very pleased.

PZ

 

[phazertwo]

From the factory PM states that the 940 is capable of 100 ipm in the x and y, and 75 ipm in the z. However I was never able to get the z to 75ipm. Sure it would run 75 ipm, but it would miss steps regularly.... and it ALWAYS misses them moving in the positive direction, which means your tool always ends up lower than it should be. NO GOOD. So one day, I was cranking the manual z crank and was thinking "damn this is tough, no wonder the motor misses steps" then I realized that the motor is turning this 90° gear and it really doesn't need too... So I tore into it, and I removed all the guts for the z manual (sorry I didn't take any pics of this). Then I built an actual real FUNCTIONAL part to block off the opening.

I had an awkward shaped piece of 0.5" black anodized aluminum that had a spot in the middle of it just perfect for the cover plate. I drilled the three holes with the closes drill bit I could find to the actual OD of the bolts, and punched the pattern in the plate, including the counter sinks. Then I was able to cut the rough shape on the band saw and bolt it to a fixture plate. Quick program to clean out the outside and it was done.

Surface finish was pretty good, though no picture ever really shows it right. Defiantly getting better at this!

After I pulled it off the fixture plate I used the pistol drill to drill the holes out to the proper clearance size and everything fit perfect. Installed in it's new home:

All and all I highly suggest this mod. It made the whole z move smoother, and MUCH quieter. Not to mention I can run 75 ipm now, without worrying about it. The only down side is that you CANNOT move the z unless you power up the machine. I make sure I always leave it in a good spot when I power down, and a few times I have had to power it up just to move the z up or down while working on the mill. Not really a big deal to me.

PZ

 

[phazertwo]

So, as it turns out, as a hobby machinist I'm on a budget. I consistently scour Amazon for tooling, and have some favorite tools I found there... here they are:

• My number one go to tool for roughing... I beat the crap out of this thing, and it just keeps begging for more. I CANNOT believe I'm still using my first one, even though I have had to use a punch to remove aluminum from the flutes at least three times.
  • https://www.amazon.com/gp/product/B01AOE7DBU/ref=oh_aui_search_detailpage?ie=UTF8&psc=1
• Same thing in 0.5" and I haven't actually taken it out of its package yet... the 3/8" just works so good.
  • https://www.amazon.com/gp/product/B00VGR6EVK/ref=oh_aui_search_detailpage?ie=UTF8&psc=1
• For finishing I've been using this carbide set, mostly the 6mm, but the 8mm works great too. For the price, this kit is unbeatable. They are 4 flute, I know a 3 flute would be better for aluminum, but they are cheap and work good, so screw it.
  • https://www.amazon.com/gp/product/B01M0W9XON/ref=oh_aui_search_detailpage?ie=UTF8&psc=1
• Last is this ball endmill set. I haven't done much profiling, but what I have done worked great with these:
  • https://www.amazon.com/gp/product/B0117A6R5S/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

You might notice that all of these tools are 4 flute, which I like because I can move faster with the same IPT, however they tend to gum up with aluminum and I have to hit them with WD-40 a lot, or just take very fine cuts. I decided to start looking into mist coolant.

This is the the story of that.

First off, I ordered a solenoid from Amazon. The Acorn’s output wasn’t rated for enough go juice to run it so a new relay needed to be installed. I had some very small relays left over from some industrial gear I de-commissioned, so I removed the fwd and rev relays that were much larger than they needed to be and replaced the with these tiny guys.
Before:

And with the new, smaller relays:

Next I got a simple mist coolant nozzle from Amazon… it’s cheap. We’ll see. I removed the factory bracket for flood coolant and built a nifty replacement out of the same 0.5” black anodized aluminum as the z cover plate. Again, it turned out awesome, and mounted right up.

The bracket:

Mounted in place:

And with the nozzle base attached:

After the nozzle was mounted, it was time to mount electronics and pneumatics. I decided that I want a regulator on this setup, so I used an old filter/regulator setup and just mounted it to the side of the machine. I also bolted the solenoid and a manifold to the machine. The manifold gives me some ports to grow into for some other cool things…

I had some water bottle sized/shaped tanks that were used to collect waste ink, and they even come with a mount! I pulled them out of the scrap pile when the company went under and have been holding onto them for 10 yrs… glad I didn’t pitch them. A simple 0.5” spacer and some 1/8NPT holes to allow air in/out and it was good to go.

The idea here is that I can control air pressure from the regulator, and coolant with the ball valve that lets air back into the coolant tank… I was worried that it would siphon coolant when the head is lower than the tank (it did), and that the ball valve would not be able to control the flow of make up air coming into the tank (it couldn't). I figured I needed to start somewhere, so I let if fly just to see what happens.

Ran the lines along with the z home switch wires, the ¼” pex tubing helped stiffen up the whole bundle which helps keep it from getting snagged on stuff… just an added bonous.


Then it was time for a test part...

Parts used:
Solenoid
Nozzle and base
Coolant

PZ