PM-727M or PM-932M - help me decide

[BFHammer]

I did want to ask, the motors that power the table, can those be used in the CNC conversion too? I'm kinda thinking not because I think the table feeds are not steppers, please correct me if I'm wrong. I'd hate to upgrade to power feed and then start all over to CNC, seems a waste.

I don't know a lot about CNC but I think you are correct the table feed motors are not steppers and I would imagine they wouldn't meet the requirements for CNC. One other consideration if you think CNC is in your remotely near future is the cost of a VFD conversion. It certainly can be done and many have been but you might search some threads I believe the consensus is that you will spend more on a VFD conversion than you would to purchase a variable speed machine up front. There are other factors to consider but worth doing a little digging before you part with any cash.

Here is a little video using my shars 2.5" facemill. I'm putting a little bevel on a brake caliper bracket I'm making for some Brembo calipers. I'm making it out of 7075t6...

Nava - Nice video, thanks for sharing - tell me more about that vise? that you're using to hold your part. It looks interesting.

 

[Astronutski]

One thing to keep in mind that can save you a lot. Check out all the tooling Matt has on the PM site. Anything you think you will need, if you order it with the mill there will be no extra shipping charge. He puts it all in with the mill. Heck just the shipping charge for a milling vise alone is around 30 to 40 bucks. Oh, and I also have the 932 PDF, and love it, but, to further confuse you, Pragmatic Lee (you tube) does some amazing work with his 727. I'm sure you will be happy with any machine you buy from Matt!! Happy Machining, JR49

LOL, not confuseled, thanks for the info, and the youtube channel I'll check him out. I have been watching a lot of CNC4XR7's channel and he has a lot of excellent info on the 727 as well.

 

[Astronutski]

I don't know a lot about CNC but I think you are correct the table feed motors are not steppers and I would imagine they wouldn't meet the requirements for CNC. One other consideration if you think CNC is in your remotely near future is the cost of a VFD conversion. It certainly can be done and many have been but you might search some threads I believe the consensus is that you will spend more on a VFD conversion than you would to purchase a variable speed machine up front. There are other factors to consider but worth doing a little digging before you part with any cash.

Ugh, haven't learnt me that much yet, but thanks, if it needs variable drive then that 30MV is starting to sound a lot better. Thanks, I'll do a lot more research.

 

[jwmelvin]

Ugh, haven't learnt me that much yet, but thanks, if it needs variable drive then that 30MV is starting to sound a lot better. Thanks, I'll do a lot more research.

From what I understand, CNC often uses pretty high spindle speeds because it uses small cutters to create a desired outline (the cutter defines the minimum internal radius of a part). The problem is that even the 30MV doesn't run all that high of a spindle speed, so it will be a little limited for aluminum with small cutters. It is better, however, than the 1970 rpm of the 932M.

I don't see why variable speed is strictly required for a CNC operation though. Perhaps someone can elaborate?

 

[navav2002]

Nava - Nice video, thanks for sharing - tell me more about that vise? that you're using to hold yor part. It looks interesting.

That's a adjustable angle plate that I got off ebay. It's just a cheep one but it actually seems like it will be OK for what I'm doing. I think I had it set @ 8 degrees in that video. They come in a few different sizes, I think mine is a 9x12 which is a nice size for the 932m...
Here's a couple of Links:
Travers
Angle Plate

 

[Astronutski]

From what I understand, CNC often uses pretty high spindle speeds because it uses small cutters to create a desired outline (the cutter defines the minimum internal radius of a part). The problem is that even the 30MV doesn't run all that high of a spindle speed, so it will be a little limited for aluminum with small cutters. It is better, however, than the 1970 rpm of the 932M.

I don't see why variable speed is strictly required for a CNC operation though. Perhaps someone can elaborate?

Alright, with the very strong desire of future CNC, I've officially thrown the 30 in the ring as a contender. And actually, the more I think about it, the more I think I will start the conversion almost immediately.

I too would love to hear the reasons for high spindle speeds for CNC, what's the "acceptable" or minimum RPM's we're looking for for Aluminum?

And is variable mandatory? The few videos I've seen I'm pretty sure the machines are not variable...... unless they did add the VFDs. Youtuber CNC4XR7 in particular.

 

[jwmelvin]

I talked to Matt at PM today regarding the 932 and 30V. In short, I’m not sure he helped me decide very much. He is very nice but I got the sense he wasn’t interested in suggesting which machine would work better for me. Part of the problem is not knowing what I need. His response is that my choice depends on which one I think I want. (?). On reflection, it is probably sound business practice to have your customers choose what they order, so they know who to blame if they have regrets later.

A few things seemed useful. His take is that motors and drives are not nearly as inexpensive as cast iron, so you give up a bunch of heft and stiffness of the 932 to get the variable-speed drive in the 30V. The higher spindle speed in the 30V is useful for aluminum and smaller cutters.

With either machine, running a higher spindle speed would require new bearings and a new motor. With the 932 you would have to convert from the gearbox to a belt drive. I didn’t clarify if the drive of the 30V would work for higher speeds with a different motor.

Other than the spindle, both are about equivalent for CNC conversion.

It would be helpful to better understand the required spindle speeds for aluminum CNC. From talking to Matt it sounded like the higher spindle speeds allow feed rates that just aren’t practical when manual milling so it’s more of a speed thing than a necessity.

Also, my idea of picking it up to save on shipping turns out to be pointless because then I would have to pay PA sales tax, which is high.

 

[sfsteel]

Looks like they just upped the price of the 30mv by $100!

 

[jwmelvin]

That stinks. Would have been nice of him to mention it when we talked Friday.

 

[Astronutski]

saw that, sucks.