[sledhead306]

I recently bought a king pdm 30 mill from a guy in town here and am looking to convert it to cnc. I have cnc experience at the shop I work at but I would like to have this unit at home to do small projects. I have looked at lot into stepper drivers and BOBs. I am looking at an mx3660 but don't know exactly what servos I should be running. also I do not have a serial port of this computer, are there more options as for USB. I have a good handle on making the ball scew conversion. Its just the electronics side that has me asking a lot of questions. open to any suggestions.

[109jb]

A PDM 30 is pretty much an RF-30. Being a round column mill you may be disappointed with it once cnc'd. I had a similar round column import mill that I converted. I then sold it and got a G0704 dovetail column mill. Even though the G0704 is lighter in weight an didn't look as beefy, it has proven to be a much better choice for CNC.

With a round column your Z-axis travel is limited to the stroke of the quill. I'm guessing it is about 4 to 5 inches on a PDM-30. This means that you will need to be creative with tooling choices due to the difference in lengths of various tools. For example, think about a 1/2" drill in a drill chuck compared to a 1/2" end mill in a collet. Your 4-5" travel can be gone right there requiring re-zeroing of the part after changing tools and raising or lowering the head. Also, for milling operations, the quill is really intended to be locked, but for CNC will need to be unlocked. When unlocked there can be a significant amount of play in the spindle.

Having said all of this, it can be done but I felt you should know some of the limitations of the round column CNC.

As for electronics, you mentioned the MX3660 which isn't a bad choice for a stepper controller. For an RF-30 sized machine you are probably on the edge for NEMA 23 vs NEMA 34 size stepper motors. Also, you said "servo" in your post, but the MX3660 is a stepper motor controller, not a servo motor controller. For size, if going with NEMA 23 motors, I would definitely go for the 570 oz-in motors. For NEMA 34, you could probably go up to 900 oz-in or so, but you need to watch out for high impedence motors. Motor selection is a tradeoff between impedence, torque, and voltage requirements. A low impedence motor needs less supply voltage for good performance. The MX3660 has a maximum supply voltage of 60V, so you would ideally want motors with an inductance less than 3.5mH. That however would need pretty much the full 60V which will increase your power supply cost. You could probably get by at 48V but with some reduced performance. The 570 oz-in NEMA 23 motor I mentioned is very popular and requires about 48V. Here are links to the Nema 23 570 oz-in and the NEMA 34 906 oz-in.

http://www.automationtechnologiesinc...kl34h295-43-8a
http://www.automationtechnologiesinc...flat-570-oz-in

Both of those motors have torque specs available. Note that the 570 motor has a flatter torque curve at low rpm where it will be used most.

For ballscrews, I would use eithe 5/8" 0.2" lead, or 1605 metric ballscrews and drive then direct. I used the 5/8 screws and bought them from McMaster Carr. The 1605 mteric screws can be bought economically with the ends machined to your specs through an e-bay supplier others have used. I forget the vendor username but someone else will probably pipe in with it. Metric or inch screws don't matter as the software will just convert it anyway.

For the quill, most round column conversions use either the stock fine downfeed motorized, or a custom screw drive which can be a problem to make. On my round column I used the stock downfeed. It worked but had a lot of backlash and I reversed the spring to help a bit which was an idea from another user on the zone. You can get a look at my round column conversion at the link below.

http://www.cnczone.com/forums/bencht...cnc-forum.html

Good luck

[sledhead306]

thank you for all the info. that was my mistake for saying servo instead of stepper. I was planning on using all the nema 34 motors I have a power supply I believe will work but it only goes to 48 volts and 25 amps. will that work with ndma 34 motors or should I be running smaller ones. I am concerned about what u mention about the round column being a problem. I haven't had any issues with lack of travel with the quill. I only use this machine with a 3/8 end mill and smaller. should I even be wasting my time on this mill or should I buy something different? remember I'm in canada and it basically costs me 1.5 times the cost over the usd price. I paid 2000 dollar cad for this pdm 30.

[Fastest1]

Sled you will be fine on the power supply. The MX max outs at 6 amps per axis. Plus not all axis in motion will be at 100% load during any machining process.

I also agree with 109 in regards to travel. With a part in a traditional vise and a drill chuck with bit in it there is little room usually. If you have the move the head all references are lost. But if you know your needs, and using an end mill is what you are doing. I would think you would be fine. Many of us build our first machine, learn a lot about what not to do and which bones to use after some time and experience. The only reason I have a round column (HF) mill is because the seller of a lathe insisted I take it as he didnt want to deal with any more people. He wouldnt let me take the lathe unless I did! I do use it from time to time but it still manual and I am going to make someone else take it ;-) I would rather have the room.

[sledhead306]

ok well the general consensus is everyone likes the dovetailed mills. I would like to learn as much as I can from your guys experience. if I were to buy a different one what would be recommended? I like the size of the pdm 30.

[photomankc]

You are already a step ahead by being willing to learn from others.

The G0704 or similar sized machine really occupies a sweet-spot for capability, size, and price. There are a number of common designations for these mills (BF20, WMD20, PM20) depending on the maker. The '20' stands for the largest drill it's supposed to be able to handle I believe in mm. I personally prefer the BF25/30 sized mills. The BF30 class is still a lot more manageable on your own than an RF-40 mill and a pretty good upgrade in mass and travel from the BF20. But that comes at a cost and group knowledge premium. There just are a LOT more BF20/G0704 owners posting info, designs, and help.

Precision Mathews PM25-MV in it's new top-mount column and belt-drive configuration looks like a really nice deal.

I would steer clear of the X2/X3 machines. They are not really bad, its just the G0704 is a lot better and more easily adapted than the X3. From what I have seen the G0704 can cut better and more aggressively than the X3 despite it's weight disadvantage.

[109jb]

I think a 48V power supply will be sufficient with the NEMA 34 motors. The torque curve for the motor I linked shows curves at both 48V and 80V. Looking at the curves I would say 48V would do the job just fine but you would sacrifice a little torque and speed, but not much.

As with all things it is a bit of live and learn. As I said I converted a round column, which made sense at the time since I had already owned it for 10+ years. The limitations of the round column were there, but I still had a lot of fun with it and made many parts with it. I now have a G0704 which is in my opinion a great value. It isn't the best machine out there but for $1200 USD it is hard to beat it for capability and machining envelope. It also has the benefit of many many users who have converted to CNC, so there is a lot of info. Converting a G0704 type machine is really a no-brainer with all of the information available. It has a machining envelope with just a few easy mods of about 18 x 8 ,x 10 which is fantastic for a mchine its size. As for cutting capability it does an excellent job on non-ferrous metals. I haven't done a tom of milling on steel pieces, but I would call it fair in that respect. If you are looking to mill mostly steel type projects you might want to consider something a bit larger like the BF25/30 mills mentioned though. I would say that if you don't anticipate doing a lot of milling of steel parts that a G0704 type machine would do nicely with the capability to do some steel work too.

I myself would like to upgrade to an RF-45 size mill at some point. I have had a couple occasions where I would have liked to have the additional rigidity and power of the RF-45, but the G0704 got the job done, just a bit slower. I also want a fully enclosed mill, but have decided that if going to the work and expense of that I would rather wait for an RF45 rather than do it on my G0704. I would also like to move to a closed loop servo control. That part is really just a personal want as the stepper controls if properly set up are just fine. The servo control is also one of those things where I could do it on the G0704, but will wait for the RF45 to do that. That brings up a big benefit of the G0704 machines though.The G0704 is small enough that I put mine on a roller base. It is light enough that moving it around is a breeze. My planned RF45 with full enclosure will be a beast. I will still have it on wheels, but it won't be such a cakewalk to move it around as the G0704 is.

I say all of this because as has been said, many of us convert a machine, learn from it and then take that knowledge and put it into another, and then another. It is wise for you to seek the knowledge from all the folks here and maybe skip one or two of those time consuming and costly steps.

Like mentioned before, the G0704 is basically the same machine as the BF20 / WMD20 / PM20, just minor differences. I just refer to G0704 because that is the flavor I have. Anything I said in reference to G0704 can be applied to the other brands.

Have a look at Hoss's site g0704.com which has a ton of information about it and probably hundreds of various videos of it cutting, and mods he has done to it. Prepare for an internet marathon though as he has tons of info to absorb.

Good luck.

[Fastest1]

109, I didnt admit to more than 1.

[photomankc]

LOL, yeah.... I bought one of those X2's myself. Luckily I only barely started down the road to CNC on it before the G0704 came along and kinda made the X2 like that girl you were embarrassed to admit you dated once.

[sledhead306]

I think u have me convinced on buying a g0704. I think I'm going to sell my pdm 30 and use the extra cash towards steppers and things

[Fastest1]

The biggest iron you can afford and fit in your location.