New PM-25MV Mill

[shooter123456]

Slow going recently with school getting near the end of the semester and all the nonsense that brings.

I ordered some new bearings for the spindle since the stock ones are getting really hot at the higher speed. I am a bit worried about these though because the spindle bearings are small. The lower is a 7007B bearing and the upper is a 7005B. The upper bearing is smaller than the upper bearing on my X2. The tapered rollers are rated at 43,000N for the lower and 30,000N for upper compared to the AC bearings which are 17,500N and 11,300N. Thats 73,000N compared to 28,800N. I don't know if that difference is going to give me a problem with rigidity, but the new bearings are rated for 9500 and 13,000 RPM, so I should be able to get the spindle going a little bit faster before it starts over heating.

I installed the new stepper drives which made a big difference. The new drives are DM542T from stepper online. The motors are running much quieter and smoother now. I no longer have any stepper hiss going on and under 10 IPM, they are darn close to silent. The TB6600s certainly work, but the DM542Ts sound much better and so far I haven't had any issues with lost steps.

The ballscrews sound rough, but I am getting below .001" backlash on the Y and around .0015" on the X. The X axis screw is currently wiggling like a freshman at her first frat party (or so I would guess, never been to a frat party...) at the floating end and the nut shakes in the holder a bit from the screw not being straight. It will definitely reduce the life of the screw and it sounds rough, but these screws were refunded and I should be able to get a year or two out of them.

I am just about done with the air cylinder for the draw bar and I have belleville springs in. The draw bar should give me between 2100 and 2500 lbs of pushing force depending on how much pressure I use. The springs are rated for 900lbs working load and 1100 when compressed. I will be running pairs so that should be 1800lbs on the drawbar with 2200 to release. I have the stock all roughed out for the air cylinder mounting and drawbar parts, I just need to run the machine to drill some holes and mill a few parts.

I have made a few changes to the design of the power draw bar as well. I have replaced the entire quill assembly with an aluminum plate that will hold a 6007 C3 bearing rated for 15,000 RPM. The spindle pulley will have one part slide into the bearing and the bore will be a close fit for the spindle shaft. That should support the spindle without needing to deal with the extra 2 large bearings. The plate will also hold the air cylinder and mount the motor. The power draw bar assembly will be floating on shoulder screws and when the cylinder is actuated, it will pull itself up until a steel plate grabs a "top hat" part on the spindle, then it will compress the spring washers and release the tool. The entire thing is made of aluminum, mostly .75" plate, except the top hat which is going to be 12L14 and the plate that grabs the top hat, which is mild steel. I probably don't need to do it with such thick aluminum plate, but the recycling center near me always has a bunch of them that are roughly 9"x30" which I pay roughly $20 for. Ordering online usually costs at least 4 times for the thinner material that would be suitable. I think it is MIC-6 or similar plate because it is definitely cast and it is very flat and consistent over the surface.

The mill has also been used to make soft jaws for the lathe so I can make the tool holders as concentric as possible. I have 8 holders partially finished now, with the .75" shank done and the undercut for the collet finished. 6 of which have had the body also roughed on the mill. Right now, I think it is 3 ER20 holders, 3 set screw, 1 face mill arbor, and 1 drill chuck holder.

Something I forgot to mention is that I tested a 2" 4 insert face mill (one of the super cheap ebay ones) with some aluminum specific inserts, and it was absolutely shredding the plate. It flung chips at least 6 feet from the mill too and took excellent cuts with an incredible surface finish. I was cutting at least .05" deep, 1.25" wide, at something like 20 IPM. I have some short videos of that that I may upload eventually.

Here are the new drivers next to the old ones. The new ones are much heavier as well, even though they don't have an aluminum heat sink (even though the TB6600s were largely for show, very little contact with the sink and the rest of the parts).

Here is the air cylinder. If you recognize it, its because its a design you can purchase from Hoss. I didn't design this one myself. Once I have it assembled and tested (its been tested and works, just have to epoxy in the seals) completely, I will chuck it up and turn the outer diameter so it is concentric and the same diameter.

Here is the air cylinder disassembled.

Some soft jaws. Lighting is terrible because the new mill is under the garage door and there are no overhead lights. The rest of the light is blocked by mill head.

Another look.

One of the jaws while being machined.

Here is a model of the new plate for the head. This part has already been machined, but I forgot to take a picture of the finished part.

Here is another look at the power draw bar model.

Another angle.

Here is a dissassembled view of the parts I need to make. They are pretty simple parts and now that the stock is roughed out, it shouldn't take long to finish it up.

I have started looking into a new motor for the spindle. I want to eventually speed it up to around 10,000 RPM which means I probably need a faster motor. I have been looking at putting a DMM servo on it, which would give me 3000 RPM continuous and 5000 top speed, which could be pulleyed to 6000 and 10,000. I am talking to them now about what those ratings mean to see if that would be a viable solution. I am also looking at 1-2 HP AC induction motors run with a VFD. I don't know if it will be worth the trouble getting the computer to control the stock spindle motor if it will be replaced soon. Once school gets out (end of next week) I start working full time for the summer, so I will have some extra money to spend.

As always, suggestions, ideas, questions, criticisms, etc are appreciated.

 

[phazertwo]

Curious what is your major?

I really like the idea of the "pinch" style PDB, especially when changing to AC bearings that are rated for a much lighter load. I think you will be okay with the lighter bearings (at least I hope so since I am doing the same thing!), just don't take massive cuts with huge tools. I would also use high quality grease and monitor the heat and vibration periodically. Generally a bearing will let you know it's on it's way out before it causes any problems. Also something to consider is a greaseable setup, so you can get some fresh grease in there every so often.

That air cylinder you built is freaking awesome. Makes me want a lathe SUPER bad...

Only question I have about your PDB/Belt drive is about the 3rd bearing. Normally, having 3 bearings on a shaft over constrains it and will cause a bearing to fail prematurely. I cannot tell by the pic if that bearing is actually constraining the spindle or maybe it's floating (the shaft is locating it). Other than that, looks like a solid design, and I can't wait to see it in action!

Also, keep us posted on the DMM servo as a spindle motor. A few others have brought it up and it's a very interesting idea.

PZ

 

[shooter123456]

Curious what is your major?

I really like the idea of the "pinch" style PDB, especially when changing to AC bearings that are rated for a much lighter load. I think you will be okay with the lighter bearings (at least I hope so since I am doing the same thing!), just don't take massive cuts with huge tools. I would also use high quality grease and monitor the heat and vibration periodically. Generally a bearing will let you know it's on it's way out before it causes any problems. Also something to consider is a greaseable setup, so you can get some fresh grease in there every so often.

That air cylinder you built i freaking awesome. Makes me want a lathe SUPER bad...

Only question I have about your PDB/Belt drive is about the 3rd bearing. Normally, having 3 bearings on a shaft over constrains it and will cause a bearing to fail prematurely. I cannot tell by the pic if that bearing is actually constraining the spindle or maybe it's floating (the shaft is locating it). Other than that, looks like a solid design, and I can't wait to see it in action!

Also, keep us posted on the DMM servo as a spindle motor. A few others have brought it up and it's a very interesting idea.

PZ

I am a microbiology major. Most people assume I would be some kind of engineering major, and if I could do the math, I probably would be. I actually think I could handle engineering now, but I have one semester left before I graduate and going to engineering would basically mean starting all over.

I will look into a way to grease the bearings. They should be relatively accessible so adding a grease nipple somewhere shouldn't be too difficult. I will cross that bridge when I get there I suppose.

Thank you for the kind words about the air cylinder. It was a bunch of work, but it was fun to make and saved me a ton of money over buying one. Looking at the tormach PDB, I should be saving around $640 by building from scratch.

The top bearing should be located on the shaft. I am hoping to have a good bit of play in the plate, so I can position it where the spindle shaft wants to be, then secure it. It is only there because I thought it might be problematic having heavy belt tension on that part of the shaft, unsupported. The belt will be pulling on the shaft 6" from the upper bearing (I guess middle bearing if we consider three bearings) and the spindle shaft gets as thin as .1".

I spoke with a guy at DMM and the set up he recommended was about $500 and he said performance would be similar to a regular AC motor with VFD, except for when rigid tapping. I might have trouble spending the extra $200ish on a DMM just for slightly better performance rigid tapping. We will see though.

 

[phazertwo]

I was thinking engineer... you have a knack for this stuff, that's obvious.

I wonder how well a DMM will work for ridged tapping when run through a belt drive. I know that Centroid says that the encoder must be on the spindle, at 1:1 in order for ridged tapping to work.

Here is what I think I'm going to do for spindle bearing greasing. It's going to require a new seal housing, but that shouldn't be any big deal. Just add a little bit of 1/8" copper tubing and you should be good to go.

For the lower bearing I think we can just go right through the quill. We would need to re-design the cap at the bottom of the quill to have a seal, but again, shouldn't be too big of a deal.

PZ

 

[shooter123456]

Wow, that is a detailed model. It looks excellent! I will have to look into rigid tapping and such a little bit more. The DMM rep said that the motor can run continuously at 5000, but that leads to a 50% drop in torque. So I could do 2 to 1 and have 6000 rpm with full torque, and 10000 with half. It may end up being too much trouble, and I can just make a tapping head instead.

Do you have any plans for a 1 shot oil system? I am thinking that somewhere down the line, I will need to add that, as well as something to grease the ballscrews.

 

[shooter123456]

I finished all of the parts that will be done on the mill for the power draw bar. It is a total of 7 parts. I just need to make 3 parts on the lathe (top hat, spindle pulley, drawbar) and this thing will be ready to go. I also milled steel on the mill for the first time and it cut very well, even with my worn out 4 flute carbide end mill. I need to come up with a way of supporting the parts better, because when I cut the slot, it deformed with the following passes and led to a slight angle on one of the sides. Shouldn't affect the part function at all though.

Here are the 7 finished parts. The steel one is the bottom left.

These two are the first cuts I did on the steel plate. I tried to capture the finish as best as I could.

Here it is cutting one of the parts with a 3 flute .125" end mill.

Here all the parts are just stacked up waiting to be screwed together.

 

[phazertwo]

Damn dude, you work fast. Good looking parts too. You're really making me want to get some more spindle time!

The model is coming along, I've decided to include as much detail as I can so I feel more comfortable designing parts to the model.

My machine has an automatic oilier, so I don't have to worry about it. Mine came with the machine so I don't know how much it cost, but it's nice to have. Right now it's on a timer, but I plan to change it over so the Acorn is controlling it, so it will only count time that the machine is actually moving...

PZ

 

[shooter123456]

PZ, you must have jinxed me. I was booking and cooking with this stuff until you said I work fast. Then no progress for a month. Had to deal with finals, then I took a trip out to Vegas to see my parents, so no time to work in the shop.

Got most everything done for the power draw bar now. I made a new drawbar, new spindle pulley, and finished machining the air cylinder. I got everything assembled and test fit and so far everything seems like it should work.

Chucked up the cylinder to turn everything to the same diameter.

Here is the finished product. I left a bit of extra material at the top because I thought the air tube connector threads would be getting a little too close to the edge. I don't think it makes it look bad though.

The new draw bar, just before being threaded. The threads on my R8 collet aren't straight, so its a bit of a challenge threading it on on the mill, but it works.

Here is everything up for the test fit. So far, everything seems to fit right. I apologize for the picture quality. The glass covering my phones camera shattered and I haven't replaced it yet.

All that is left is the top hat for the spindle, and I will be ready to try it out. Fingers crossed that it goes well.

 

[phazertwo]

Sometimes life just pops up. Again, nice looking parts!

PZ

 

[tcarrington]

A very nice addition to a very nice small mill. I think a time / motion study will show changing tools is a large contributor. Have a consistent pressure on the collet might also be an advantage. Great job!