New PM-25MV Mill

[shooter123456]

If you stated earlier, I am sorry if I missed it. What are you building this machine to make? Are you trying to get in the machine shop business? Make your own products you plan to sell?

The machine is for personal projects, I am just trying to make a few things to sell to fund more parts for the machine. Not planning to get into the machine shop business.

 

[adhue587]

Hi,

You've done an awesome job at getting this designed. Any chance you would share your 3D models?
I have a PM-25MV and really want to get it CNC ready. The Power Drawbar and ATC are awesome too.

 

[shooter123456]

The new servo motors got in. I got 2 CPM-SDSK-2321S-RLN motors for the X and Y axis and CPM-SDSK-3421P-RLN for the Z. Needless to say, they are quick! I am using the same 48V power supplies I used for the steppers, so the motors are limited slightly from their full ratings at 75V. I am probably going to buy a Clearpath power supply sometime soon to get them up a little bit and to run it off of 240v AC input since I have a 60 amp line for it.

I am now getting 400 IPM rapids on X and Y and 250 on Z. The set up was very easy and they are very smooth. They are also much quieter than steppers. You usually hear the ballscrew turning now instead of the stepper whine. They are plenty strong for this machine and I am very please.

Here is a video showing a short before and after.

 

[phazertwo]

Very nice! I like the speed, it really is impressive. I'm very excited to see you tear up some Al.

Care to share why you went with Clear Path?

PZ

 

[shooter123456]

Very nice! I like the speed, it really is impressive. I'm very excited to see you tear up some Al.

Care to share why you went with Clear Path?

PZ

Thank you!

I went with clearpath for a number of reasons. I was really only considering them and DMM because I wasn't aware of any others that weren't either no name Chinese imports or 3x+ the price.

Clearpath won because:

1. The sales guy was very clear and straight forward, providing me with a ton of information and making it easy to choose which ones were best for me.
2. The DMM sales guy just quoted me for the most expensive Nema 23 and Nema 34 items they had and didn't seem to think it was overkill even though they were 3x the power of what I have now. Ended up being more than $600 more expensive for very little gain.
3. Clearpath lets you try their motors for 3 months and return them no questions asked if you are not impressed.
4. Clearpath autotuning is simple and easy, the DMM ones were not nearly as straight forward.
5. I can use the Clearpath motors on my machine without buying new power supplies. Saves me a few bucks for now.
6. Drives are attached to the motors saving me space in the electronics box.
7. The information available on the Clearpath motors was much more clear and thorough than DMM. They also seemed to have their stuff together a lot more (ie their site looks professional and is easy to navigate vs DMM which looks kinda like an ebay store selling rebranded motors.)

It wasn't a super tough decision really and I am happy with the performance.

 

[phazertwo]

Good to hear they have some good customer service! A 3 month no questions asked return is a pretty sweet deal as well.

PZ

 

[Larry42]

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.
View attachment 257206

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.
View attachment 257207

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.
View attachment 257208

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.
View attachment 257209

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.

To take some strain off the Z-axis system you might install a couple of pneumatic cylinders, one on each side for balance. The regulator would maintain the same force through out the travel range. Mount the cylinders rod up to get maximum force from the piston. This is a common system on industrial CNC machines that carry much heavier loads.

 

[Larry42]

I made some new lock nuts and machined some spacers for the AC bearings. I suspect some of the .008" backlash was coming from the bearings I was using and I don't think they were preloaded properly. I made 2 piece nuts with screws that can be tightened to lock the nut down on the threads. These are much better than the lock nuts that came with the ballscrews and in my opinion, they are better than the nylon lock nuts. Since it was an M12x1 thread, I couldn't commercial nuts for it anywhere anyway. They use 3 4x40 screws to lock and I cut the holes so there was just a little bit of space between the nuts when the holes are aligned. I have always had trouble with the regular lock nuts occasionally loosening up and it has ruined parts before. I am confident that these won't move once locked.
View attachment 259216

Here it is installed on the X axis with the new coupler on the motor.
View attachment 259217

I machined some spacers so I could preload the AC bearings as well. That was pretty straight forward but I don't have any pictures of it. Essentially I machined a bar to the right inside and outside diameter, then parted off 3 pieces, then super glued each to a piece of steel in the spindle, and faced it until it was about .05" thick. Using the lock nuts, I can adjust the preload on the bearings without needing shims.

I have the tool changer mostly designed now. It will be a little while before I am ready to start making parts for it, but I will start ordering stock and parts soon. The plan is to use a Nema 23 motor, a deep groove ball bearing, some round linear rails, and a pneumatic cylinder to run it. I think I will use an arduino to control the changer if I can figure out how to interface it with LinuxCNC. The plan is to have several sensors checking each step of the tool change to ensure reliability.

The tool change will go like this:

1. Z axis return to home position (Home switch confirm head in position)
2. Spindle motor off (Relay on spindle power to ensure spindle motor off)
3. Tool changer move into position below spindle (sensor to confirm changer in position)
4. Z axis lower tool to tool changer (sensor confirm head lowers to tool tray)
5. Pneumatic cylinder release tool (sensor to confirm cylinder actuates)
6. Z axis return to home position (home switch confirm head in position)
7. Tool changer rotate to the next tool (sensor to confirm position of carousel and proper tool selected)
8. Z axis lower spindle to tool (sensor to confirm head lowers to tool tray)
9. Release pneumatic cylinder (sensor to confirm cylinder releases)
10. Retract tool changer (sensor to confirm tool changer fully retracted)
11. Z axis return to home position (home switch confirm head in position)
12. Confirm new tool in spindle (not sure how I will do this yet)

Here is the tool changer with all of the covers removed.
View attachment 259218

Other side.
View attachment 259219

On the mill.
View attachment 259220

I used Fusion360s FEA to make sure the changer wouldn't deflect too much under the weight of all the tools. It gave me a deflection value of .0002" at the worst position so I am confident the structure is strong enough.
View attachment 259221

With a vise installed, there will only be about 5.5" between the bottom of the tool holders and the top of the vise jaw. I am considering a few alternatives such as adding a Z axis to the tool changer so it lifts up and out of the way when not in use, and the table can move all the way forward (closest to me) when changing tools, so hopefully it will be mostly out of the way. I don't think it will be too much trouble though, since I don't plan to have any tools sticking out more than 2 inches, and I don't often work with parts sticking more than 3.5" out of the vise. Im pondering the idea of some kind of quick release for the tool changer so I can lower the tool carousel out and remove it completely for when I work with taller parts.

If anyone has any ideas or suggestions, I am all ears. I have never tackled a project like this and could use all the help I can get.

Some machines mount the tool changer separate from the head. Off to the side. The machine then transverses to the end of its (X) travel to pick up tools.

 

[shooter123456]

To take some strain off the Z-axis system you might install a couple of pneumatic cylinders, one on each side for balance. The regulator would maintain the same force through out the travel range. Mount the cylinders rod up to get maximum force from the piston. This is a common system on industrial CNC machines that carry much heavier loads.

That seems to be a common solution for this sort of problem. That motor was swapped for a 1200 oz in stepper, then swapped again for a servo. Now the motor is more than capable of moving the head.

I still considered going that way to relieve strain on the system and prevent unnecessary wear, but when I did the math, it wasn't really worth it. The head weighs about 75 lbs with everything on it. The air cylinders would only be able to counteract gravity, otherwise they would be pushing up against the motor and the head would be floating. Not ideal. At 75 lbs, the head experiences 333N pushing down. The ballscrew is rated for 9800N. So really nothing to worry about there.

Some machines mount the tool changer separate from the head. Off to the side. The machine then transverses to the end of its (X) travel to pick up tools.

I also considered doing that, but elected not to for a few reasons. First, it takes up table space, which this machine does not have much to spare. I think on the one I modeled up, to get 9 tools on the table, I lost 6" of travel in the X, then a little more to keep the tool from hitting the rack when it was cutting. The other issue I had with that is keeping chips away from the tools. I wanted to keep the tools up out of the way to keep them a bit cleaner and hopefully prevent chip build up from gumming up the works.

I am very close to done with a rotating tool changer that will be mounted on the column. It is a very common design on industrial machines, so in theory it is a tried and true method.

I appreciate your input though for sure!

 

[Larry42]

That seems to be a common solution for this sort of problem. That motor was swapped for a 1200 oz in stepper, then swapped again for a servo. Now the motor is more than capable of moving the head.

I still considered going that way to relieve strain on the system and prevent unnecessary wear, but when I did the math, it wasn't really worth it. The head weighs about 75 lbs with everything on it. The air cylinders would only be able to counteract gravity, otherwise they would be pushing up against the motor and the head would be floating. Not ideal. At 75 lbs, the head experiences 333N pushing down. The ballscrew is rated for 9800N. So really nothing to worry about there.



I also considered doing that, but elected not to for a few reasons. First, it takes up table space, which this machine does not have much to spare. I think on the one I modeled up, to get 9 tools on the table, I lost 6" of travel in the X, then a little more to keep the tool from hitting the rack when it was cutting. The other issue I had with that is keeping chips away from the tools. I wanted to keep the tools up out of the way to keep them a bit cleaner and hopefully prevent chip build up from gumming up the works.

I am very close to done with a rotating tool changer that will be mounted on the column. It is a very common design on industrial machines, so in theory it is a tried and true method.

I appreciate your input though for sure!

I've got two CNC's with tool changers. One is a ride-along with 8 tools that is located just in front of the spindle. The other is mounted at the end of the moving gantry and holds 18 tools. It has a cover built in. 8 tools isn't enough. If an operator has to put a different tool on the changer, he has to be sure to have told the machine the diameter and length or bad things happen. I can see where adapting a manual mill to a tool changer in a way that wouldn't limit the table movement would add design complications. It could be done by having the tool carousel move into and out of it's tool changing location.