New PM-25MV Mill

[shooter123456]

After getting some Christmas money and making a few extra bucks with a machining job, I decided to get a new milling machine. I currently have a Harbor Freight X2 that I have had for a little over 2 years now. I will be converting the PM-25 to CNC immediately. I intend for this thread to be similar to my PM1030v thread where I try to share details about the machine that I didn't find before buying it, get help with things that aren't quite right, and share what I find the machine is capable of.

I currently have all the CNC components from my X2 and they should be sufficient for the PM-25, except the X axis ball screw which will only allow for 17 inches instead of the full 20. That will be replaced relatively soon.

It will be converted and upgraded in 3 stages.
1. CNC Retrofit
-400 oz-in steppers on each axis
-1605 single nut ballscrews
-TB6600 drivers
-Control with LinuxCNC

2. Automatic Tool Changer + Spindle speed increase
-10 Tool Umbrella Changer
-Pneumatic Cylinder
-TTS Style Holders
-Angular Contact bearings in the spindle
-New Pulleys

3. Full Enclosure similar to Tormach 440

A few reasons I chose this mill specifically:
1. PM customer support and 3 year warranty. After my experience with the lathe, their quick responses (The longest it ever took to get a reply was 12 minutes), and their quick shipping of parts covered under warranty.
2. Most parts from my X2 can be reused for the CNC, then I can revert the X2 to manual.
3. Size. My shop is currently a 2 car garage that needs to be able to get a car in if necessary. Right now I have 2 lathes, a mill, a grinder, a work bench, drill press, and band saw in there and it is getting full.
4. Belt Drive. I was also considering the G0704 and PM-727. I didn't want to have to deal with making a belt drive for the spindle or taking apart the head to get the gears out.
5. 120V power. I was considering the PM-30MV because it has a 2 HP motor instead of 1, has a few extra inches of travel in each direction, and weights nearly double what the PM-25 weighs. But with 220v power and a breaker box that is full, I would need to hire an electrician to either put in another breaker box or rewire it somehow to make space. With the cost of the rewiring, the need to buy all new CNC components, and the extra cost of the mill, it got pushed too far out of my budget.

The machine shipped yesterday and I got the call this morning that it will be delivered this afternoon. If the truck arrives before 4:06 PM, it will have shipped from PA to NC in less than 24 hours. I elected for the lift gate delivery this time since I no longer have access to a truck and a trailer.

I have plans for some extras for this machine that I think will be fun.
1. 4th axis, either a trunion table or just a chuck.
2. New spindle for a BT-25ish tool or something entirely custom.
3. Servos (maybe)
4. A touch probe
5. Flood coolant
6. A control panel

Right now, the delivery is scheduled for between 4pm and 6pm, with the estimated arrival time of 4:26 to 4:35. I will post pictures and more details this evening when it gets here.

 

[7milesup]

Sweet! Will be watching your thread.

I have been thinking about converting my 833T to CNC, but the finance department would become significantly cranky(er)...

 

[tweinke]

Will be watching this, learned a lot from your 1030v thread.

 

[shooter123456]

The machine was delivered yesterday without any issues. I was going to upload pictures last night but imgur was having server issues. I will have to keep it brief, but I will add more details later.

The driver had a 48' trailer that managed to turn around in a cul de sac. If you have never seen that, it is really impressive. Hats off to that guy managing to get into a residential street, unload the machine and drop it in the garage, and get the truck turned around in about 10 minutes.

The machine was crated well and arrived without any damage. Here is a picture of the crate on the pallet.


With the crate taken apart. Everything looking good.


I had to take the table and head off in order to lift it onto the bench. No engine hoist and no one to help lift. While I was taking the head off, I got a picture of the underside of the base casting. Its a much higher quality casting than the X2 I have. You can also see the Y axis leadscrew in there with the brass nut. The machine has 20mm leadscrews.


I took the table off which wasn't difficult. It slid along very smoothly and popped right off at the end of travel. I weighed the table at 66.7 lbs with leadscrew. The head weighed in at 56.9 lbs. I gotta say, the bottom of that table is gorgeous. The ways are ground and you can only see faint traces of machining marks in a few places. The rest is ground completely smooth. The leadscrew is also 20mm and is about 30 inches long. Table travel without overshooting the ways is 20.5".


If the machine weight of 265 is correct, that means column, base, and saddle weigh in around 140 lbs. It was heavy so I didn't want to put it down on the scale once I picked it up. I just lifted and placed it up on the bench. Those parts along weighed more than my entire X2. Definitely a beefy machine and a large step up. Right now it is on a fish tank stand I built. It supported a 30 gallon tank for 2 years so I know it can handle the weight, but it will ultimately be replaced by a dedicated stand.


It has oil channels machined into the ways which should make it easier to prevent the machine from binding. You can see the holes for attaching the X axis nut, and the hole in the fire side way is for attaching the Y axis leadscrew. With that position, it loses about an inch of travel on the far end, and it has to over travel the ways by about 1.5" to get the full 7" of travel. The Y axis also slid nicely without any binding.


The base dovetails look fantastic as well. Definitely ground all around. That grease looking stuff on the ways felt like some kind of glue. It didn't come up with acetone or isopropyl alcohol, so I am not sure how to get it up. I am not sure what those markings in the top ground surface are. You couldn't feel anything raised or depressed there, so its either a casting defect or light scratch.


The head went back on without any issues. I placed it on its side on a block of wood, then just positioned the Z axis saddle and pushed it into place. The Z axis slid well, but it is exhausting turning that handle to lift the head and lower it. The chip guard is attached to a switch so if the guard is open, it won't start. But that cover immediately hit the vise when I tried doing some test cuts. So the whole thing was removed and luckily the switch defaults to on, so if you pop the bar out, its fine.


Test cuts went pretty well. It machined nicely and the motor was able to put out decent torque. I didn't push it too hard but it chewed up some aluminum for a few minutes. The motor speed fluctuates a little while I was turning handles, but usually kept within about 30 RPM. I didn't cut much, I just wanted to make sure everything would work before going ahead with CNC. I need to learn how to adjust the gibs correctly because there were a few points where it started to chatter a bit inexplicably with heavier cuts, but I was satisfied with its performance.


The motor is a 2500 RPM motor and the high speed is a 1:1 drive. I had asked PM beforehand what the RPM of the motor was and they said they think it is 5000 but they are not sure. I don't think there is going to be room to get a 2:1 belt drive to get the spindle up to 5000, unless I make a new motor mount. That isn't a big deal though. If it was, I would have asked to know for sure before I bought it. The motor also makes a bit of a clicking sound as it rotates. Im not sure if that is normal. It is quieter than my brushed motors except for that clicking. I haven't measured spindle runout yet. In the electronics box, the power button wasn't installed all the way so it was loose. I popped it all the way in and that was fine. I tried to figure out who makes the motor and controller to get some specs on them, but neither had any markings that I could find. The spindle is controlled by a potentiometer, so I think I can swap that for an electronic pot to control it. I also noticed the E-stop button was significantly lower quality than the E-stop on my lathe. The lathe e-stop, you just twist to release and it pops out. On this one, it doesn't feel spring loaded so you do all the twisting to get it to release. It just doesn't feel as nice or as solid as the lathe e-stop. It also feels like much cheaper and flimsier plastic. I am also not a huge fan of where that is positioned. On the X2, it was positioned on the right side of the box and on the lathe it is right on top. This one is kind of tucked in a corner and partially obstructed by the mounting for the chip guard. When something is going wrong to the point that you are reaching for the EMERGENCY stop, and not the regular stop, I want it to be unobscured and easy to get to.

A few perks though that I wasn't expecting: The toolbox is a much nicer one than came with the lathe. It is plastic with a nice handle on top and a clear top compartment. The lathe came with a sheet metal one that is fine for what it is, just not as nice. The oiler is also way nicer. The one that came with the lathe leaked more oil than it dispensed and the nose didn't fit into the oilers. This one is a plastic squeeze bottle type and the nose fights right into the oil holes. It didn't leak at all when I used it.


There is also a drain with a hose attachment on the table for draining flood coolant. There is a machined recess at the top that is at a slight slant so it will drain out. I thought that was a nice touch and I wasn't expecting it. The table also had a t-slot at the front that had stops installed. The T slot would have been useful for installing a DRO if this machine was going to have one. They also used some kind of sticky yellow glue to protect the table, instead of a grease. It took a bunch of acetone to get it off and I haven't gotten all of it off yet.


I may be needing new ballscrews immediately. My X ballscrew is 550mm (21.5 inch) vs the 30" leadscrew. That may leave me losing more travel than I thought. The Y axis ballscrew is 11.9" and the leadscrew is about 13, so that one might be ok.

I have AC bearings ready for each axis and I think they will be sufficient. I think I will end up upgrading the Z axis pretty quick with a 20mm screw and Nema 34, so I will need new AC bearings. I will have to figure out how to preload these bearings right as well.

 

[shooter123456]

How to remove the Z axis leadscrew on a PM-25MV mill. (I couldn't find it by googling, so hopefully the next guy can find this)

It took me a while to get the Z axis leadscrew out because of the way the miter gears are installed. Turns out, you need to remove it all in a pretty specific order.

Step 1. Lock the Z axis gibs so the head stays in place. It might be a good idea to put a note or mark somewhere so you don't forget the leadscrew is out, then unlock the gibs and have the head fall.

Step 2. Remove the column cap.


Step 3. Remove the lock nut from the Z axis lead screw while holding the Z axis handle to keep it in place.


Step 4. Remove the set screw holding the smaller miter gear to the shaft.


Step 5. Tap the shaft out from right to left. The Z axis handle will come out with it.


This is what that shaft looks like with the handle removed, but it does not have to be.


Step 6. Remove the large miter gear from the Z axis lead screw.


Step 7. Remove the key in the Z axis lead screw. If you try to drive it out before removing the key, you will break a thrust bearing. This is what the shaft looks like.


Step 8. Remove the screw from the Z axis saddle that holds the lead nut in place.


Step 9. Jiggle the lead screw until you get it to drop free, while holding the nut so you can lower it down.

Step 10. Once the leadscrew is free, remove the 4 screws holding the handle plate in place. Then pull straight out. There are roll pins in place so it can only be pulled straight out.


Step 11. While holding the nut from the front of the column, unscrew the leadscrew until it is free of the nut. Pull the screw out and then pull the nut out.

Step 12. Nap time, cuz that was exhausting.

 

[shooter123456]

I have had the chance to play with the mill a bit more and get started on the CNC parts. I forgot just how much fun it was turning handles and how fast simple operations can be.

I modeled up the conversion parts I will be using. I am going to need to make 15 total parts. I am currently shopping for a new X axis ballscrew with double nuts and a nema 34 for the Z axis.


The machine is very capable and leaves a very nice finish in aluminum. It has been able to hold .001" without much effort on my part. If I tried a little harder, it would certainly do better.


A couple of weird things I have experienced so far:
1. When I lock the X axis gibs, the Y axis tightens up and becomes harder to turn. The only thing I can think of that would cause that is the saddle distorting when the gibs are tightened.
2. There is a point on the X axis where it starts chattering a bit in deep cuts. It is only about half an inch that it happens so I figure it must be something with the leadscrew, or maybe a low spot in the ways.
3. There is a slight delay from the spindle motor when you start a cut. When the cut starts, it pauses for maybe half a second while the RPMs drop, then it jacks up the torque and gets the spindle back up to speed. It takes way longer for this motor to respond than the brushed motors I have used.

 

[shooter123456]

Motors are mounted and axes are moving. Looks like my careful measuring at the beginning paid off because every part went on without an issue and the machine moves smoothly.

Here is the Y axis motor mount. The ballscrew I have on the Y is about an inch too short so I am down to 6" of travel. When the funds allow, that will be replaced with a longer double nut screw.


Here is the X axis mount. The picture isn't very good because the lighting is bad. I need to get some more light over in that corner of the garage. The X axis loses 5" travel with the current ballscrew. This one will also be replaced with a longer double nut screw when the funds allow for it.


Here is the Z axis. This unfortunately isn't going to last as long as I hoped it would. The 400 oz in motor didn't have the torque to reliably move the head. The motor would not lift the head under 60 IPM or over 120. At 50 IPM, it would try to move it, maybe make a quarter of an inch, then the head would fall as the motor strained. At 75 IPM, it would move the head well, but would stall roughly 10% of the time when it was lifted. I am looking at Nema 34 motors and drives now to replace it. I think I will make a simple adapter plate to allow the Nema 34 to mount to the Nema 23 mount. I am thinking somewhere in the 900-1200 oz in range. Since there will be a pneumatic cylinder and potentially a larger motor on the head, I want to have a little extra power so I can move it quickly without needing any counter weight or spring helping to push the head up.


I was hoping the 400 oz in motor would last a little while on the Z axis, but my hand has been forced. I was getting set up to do some test cuts when something exploded inside the power box. The Z axis drive ate it, potentially from the current being drawn holding the head up. So until I get the new motor and drive, I won't be doing any cutting on the machine.


I have started the design work for the tool changer and have plans for a pneumatic cylinder, so hopefully those will be next. I am also getting the planning for the enclosure started. I got used to it with the X2 and doing the manual machining made such a mess I don't know how long I will last without one.

 

[shooter123456]

I got a new driver and tested it out with the existing motor on the Z axis. Using the same input voltage and supplied torque, the new driver is able to move the head without any trouble. I got a DM860T, and wow it is a world different from the TB6600s. The motor is much quieter, there is no stepper hiss, there is no start up jump, it produces more torque and it runs much cooler. Moving the head at 30 IPM, it is nearly silent. When I step it up to 100 ipm, it makes a stepper noise, but it is much quieter and lower pitched (think errrrrr instead of eeeeeeeeeeee). The only weird thing is the motor makes a strange grinding sound at 150 IPM, and only at 150 IPM. Thats 750 rpm on the motor or 12.5 rps. There might be some resonance there causing that issue.

I am very strongly considering swapping the TB6600s on the X and Y with DM542T drives. If they run the same way the DM860T does, it will be much smoother and much quieter at lower speeds, and produce much more torque from the same motors.

Here is the new driver next to the blown one.



I did some test cuts with the new driver on the Z, and I am very please with the machines performance. Using a .375" 3 flute carbide end mill, I was able to make .1" WOC, .75" DOC, up to 38 IPM at 2500 RPM. That is an MRR of 2.85 cu-in/min. It handled it without chatter, but the little slip in spindle speed while the motor catches up did cause some vibration. I wonder if there is a way to reduce that delay in spindle speed during heavy cuts because with an adaptive tool path, it is constantly loading and unloading the motor and it is very noticeable when the RPM fluctuates. It made some nice big chips like that.


I also ran the first part under CNC control. It was supposed to be an electronics enclosure for my micro lathe. Unfortunately, the X axis lost a bunch of steps very quickly with the first cuts, so the part will be scrapped. I am not sure what caused the lost steps, but making the cuts less aggressive, it was able to run without losing any steps.

Here is the first precision scrap produced on the new machine.


I also have a bit of a backlash issue to deal with. Each axis has about .008" of backlash, but on the old machine with thrust bearings, it was usually .002-.003. That makes me think the bearings I used on this one are causing that backlash. I need to get new shims to put the AC bearings in (I don't know if I mentioned I am using the deep groove bearings that came with the ballscrews at the moment), and I am currently sourcing some double nut ballscrews. Both should hopefully reduce the backlash below .0005".

 

[phazertwo]

Seems like you're pushing the Z pretty hard to be running it 150 IPM. Remember that with a stepper as your speed goes up, your torque goes down, so you're far more likely to loose steps while moving fast. Most times I have missed steps was because of a rapid move, I eventually found a speed/accel. that worked then backed it down another 20% (125IPM X and Y to 100IPM). For what it's worth I also have DM860's but with 600oz-in motors on the X and Y although I have a PM-940 which I would assume is quite a bit heavier. At the end of the day it made more sense for me to run a bit slower than scrap parts.

The other scenario I have lost steps in was not using smoothing in Fusion (and the built in smoothing in my controller). When I'm roughing I set smoothing to 0.005" in fusion, and then I set it to 0.0005" for finishing. You can hear the difference in the machine, it literally sounds smoother, and you can tell it's not working as hard.

Your build looks very nice, I'm excited to see where it goes and it's making me think hard about re-building some of mine!

PZ

 

[shooter123456]

I appreciate the input Phazer. I did a bit of math, and your mill is at least 4x as heavy as mine, so the head is likely a good deal heavier as well. I was actually able to run the head up to 240 IPM before it would stall. It was pretty reliable at 160, and worked at 150, the motor just made a weird sound. It made it going up and going down, so I don't think its from the motor straining too hard under the load.

It was the X that was giving me trouble with lost steps, and when it was losing them, it was going less than 20 IPM since 20 was the feed rate, and it was currently arcing with the Y axis. It could be a resonance issue that caused it to lose torque only at that specific speed in the arc, and then the force of the cut was able to overcome the motor. In theory, it should have had more than enough torque at 15-20 IPM if it could accelerate the table to 360 IPM at 60 IPS without stalling. I will try to figure out what the deal with that is though, even if it just means replacing the ballscrew and drivers, which will happen anyway.

I appreciate the kind words. I am very excited about this machine and my plans for it seem to keep growing.