PM-833TV CNC Conversion Accuracy?

[Beantown]

You guys were a great help in talking me into a new PM-1440GT (should be here soon!), so now I need some help on the mill! I’m currently leaning towards the PM-833TV but considering the PM-935TV. I have read, but probably not retained, just about everything I could these two mills. It sounds like I really couldn’t go wrong with either. However, I do have a few more questions based on what I have read.

Before I dive in and start rambling I wanted to share my constraints & requirements as to why I'm looking at these mills. I'm certainly open to alternatives as long as they meet the following:

• I am very limited on space. The PM-935 is as big as I can go, and to be honest I’m pushing it.
• I would like the best quality and capable machine I can get in this size, but I am willing to pay more (within reason).
• I would like to be able to convert to CNC in the future.
• I want something new that I can easily ship to my home and I don’t want to wait around to find a unicorn. Equipment like this does not show up in my neck of the wood often, and I don't have time to drive across the country.

For either mill, I don’t think I’ll be hogging steel with a ¾” endmill a ton, so It feels like I’d be better off with the variable speed version of either mill. That is better for the CNC conversion, but based on what I read about the dovetail heads it sounds like a CNC conversion wouldn’t be a good idea at all. If the dovetail head could introduce 0.003 or more in inaccuracy, why even bother? I can get better accuracy with my CNC router. When people do the CNC conversions are they just accepting this or are they able to do something to make it better? None of the videos or write-ups address this concern. If this is true, then I might as well abandon my CNC dreams and go with the PM-935?

 

[matthewsx]

Can't answer the question about accuracy, but my vote is for a knee mill over a square column benchtop. Here are some threads about converting the 833 to CNC,

Search results for query: 833 cnc

www.hobby-machinist.com

@davidpbest did an extensive write up of the pros and cons of your two choices.

Ridgidity - 833TV vs. 835 vs. 935

Which machine is more ridgid and can handle larger end mills, can hog largest amounts of steel, can handle hardened steel better? I've read a few times about the ridgidity issues with J head knee mills when compared to square column bench top mills like the 833. I've narrowed it down to...

www.hobby-machinist.com

John

 

[Beantown]

Can't answer the question about accuracy, but my vote is for a knee mill over a square column benchtop. Here are some threads about converting the 833 to CNC,

Search results for query: 833 cnc

www.hobby-machinist.com

@davidpbest did an extensive write up of the pros and cons of your two choices.

Ridgidity - 833TV vs. 835 vs. 935

Which machine is more ridgid and can handle larger end mills, can hog largest amounts of steel, can handle hardened steel better? I've read a few times about the ridgidity issues with J head knee mills when compared to square column bench top mills like the 833. I've narrowed it down to...

www.hobby-machinist.com

John

Thanks! Yep, read all of those!

 

[Beantown]

Okay, after hours more reading....I don't think I want to buy a mill based on converting is to CNC in the future. I'll start with a manual and look into a different CNC unit when the time comes. I think I really want a manual lathe to start. I'm learning toward the PM-935TV. I really like the idea of the ACRA 9x42, but I think it's just too big and heavy for my shop. Is PM the only game in town for the 4/5th size knee mills?

 

[matthewsx]

Okay, after hours more reading....I don't think I want to buy a mill based on converting is to CNC in the future. I'll start with a manual and look into a different CNC unit when the time comes. I think I really want a manual lathe to start. I'm learning toward the PM-935TV. I really like the idea of the ACRA 9x42, but I think it's just too big and heavy for my shop. Is PM the only game in town for the 4/5th size knee mills?

CNC conversions can be done really well, but unless you have a need it’s really just another hobby. There are plenty of shops out there that will bid on one, or 10,000 pieces better and cheaper than you can do in your home shop.

That said, Tormach makes some really nice small CNC mills and lathes for not too much more than a good conversion starting from new would cost.

I do have a CNC mill/drill project I hope to get back to someday. Now that I have a real mill it’ll be easier to make the parts I need to fix the shortcomings I built into it in the first place.

I found my baby Bridgeport (Samson) on the local Craigslist. Saw it change hands the first time and when that owner decided to sell I jumped on it. Actually it sat there overpriced for a month before I called and made a deal.

I truly don’t have space for a full sized mill so this one is the biggest I can fit and still have room for other tools. As for new, I think PM is probably your best/only shot. The ones Grizzly sells are on pedestals, so not really as big although I haven’t seen either in person.

They did sell quite a few of them in the 1980’s. Taiwan built and quite acceptable as small machines. A world of difference from the RF30 I had before.

Good luck and Merry Christmas,

John

 

[wrmiller]

I did precision pistolsmithing and fabrication on my little PM935TS w/VFD for over 5 years. The machine is more than capable, if the operator does their part. And zero issues with it. Great little mill IMO.

 

[Beantown]

CNC conversions can be done really well, but unless you have a need it’s really just another hobby. There are plenty of shops out there that will bid on one, or 10,000 pieces better and cheaper than you can do in your home shop.

That said, Tormach makes some really nice small CNC mills and lathes for not too much more than a good conversion starting from new would cost.

I do have a CNC mill/drill project I hope to get back to someday. Now that I have a real mill it’ll be easier to make the parts I need to fix the shortcomings I built into it in the first place.

I found my baby Bridgeport (Samson) on the local Craigslist. Saw it change hands the first time and when that owner decided to sell I jumped on it. Actually it sat there overpriced for a month before I called and made a deal.

I truly don’t have space for a full sized mill so this one is the biggest I can fit and still have room for other tools. As for new, I think PM is probably your best/only shot. The ones Grizzly sells are on pedestals, so not really as big although I haven’t seen either in person.

They did sell quite a few of them in the 1980’s. Taiwan built and quite acceptable as small machines. A world of difference from the RF30 I had before.

Good luck and Merry Christmas,

John

Merry Christmas!

Yea, this is more about the learning experience for me than anything. It's a very expensive hobby, but it brings me more joy than anything else of this nature. I couldn't build a CNC for the return on investment....I make Bernie Madoff look like Warren Buffett.

CNC has it's appeal because I know I can do so much more with less real skill. I know how to program toolpaths....but complex setups on a traditional mill is going to be a learning curve. It will be fun, though.

 

[Tipton1965]

I really like the idea of the ACRA 9x42, but I think it's just too big and heavy for my shop.

You probably already know this but big and heavy are good things for a mill to have. Not trying to knock PM machines but if you have the means I wouldn't hesitate to go for the ACRA mill. I originally purchased a PM 833 and although it was a perfectly fine machine, I couldn't get past the differences in operation compared to a knee mill. I learned on knee mills when I did my apprenticeship years ago. I ended up selling the 833 and bought an ACRA knee mill and couldn't be happier.

On a side note. My experience with PM was excellent, from delivery to after the sell service.

 

[Beantown]

You probably already know this but big and heavy are good things for a mill to have. Not trying to knock PM machines but if you have the means I wouldn't hesitate to go for the ACRA mill. I originally purchased a PM 833 and although it was a perfectly fine machine, I couldn't get past the differences in operation compared to a knee mill. I learned on knee mills when I did my apprenticeship years ago. I ended up selling the 833 and bought an ACRA knee mill and couldn't be happier.

On a side note. My experience with PM was excellent, from delivery to after the sell service.

Yep, totally understand that. I just have to draw the line somewhere. That ACRA is 1000lbs more....There is no doubt it would probably be better, but I'm not sure I can manage that weight in my shop. The PM-935 is already pushing it. My worry is this new hobby is going to end up costing me way more than I ever expected. I have been toying with the idea of moving now....so I can build a real shop. LOL.

 

[Tipton1965]

That ACRA is 1000lbs more....There is no doubt it would probably be better, but I'm not sure I can manage that weight in my shop.

You can move it around with a simple pallet jack no problem.