PM935TV

I really love that 7 x heavier thing.
Are you sure about your cost comparison?
How do you add it up? Mine didn't cost over $8K with 3 power feeds (not counting the spindle feed) and a DRO, but then that was couple of years ago.

I bought my 833S to replace a Seig mill and the difference is indescribable. I wanted to buy my last ever mill and this seemed to fill the bill.
Even so there are things I do where even more rigidity (and probably weight) would be welcome. I would certainly never go back to a bench mill unless I was planning to do a CNC conversion and even then I would think twice.
 
I put every option, including installation where possible, in my cart for each. That's how I came to the cost difference. Granted, the installation for the power feed installs isn't an option on the 833 but I'd order the 935 installed so it's a fair comparison (only) to me.

The LMS 3990 is, essentially, a Seig built to better standards. Mine has a variable drive and I put on an X power feed and a spindle stop for the drawbar. I can only imagine the difference between it and the 833.

I placed an order for the 833TV today. It'll take a couple weeks to install the DRO so I'm looking at mid-March. In talking with PM, they have to clean the cosmoline to install the DRO so that alone is worth the cost. I'd pay them to remove all the cosmoline before delivery. I wish that were an option!
 
Congrats on the 833TV. Comments and pics are required when you get it. :D
 
Regarding a power drawbar setup, I found Priest Tools which makes things specifically for PM and LMS mills. I talked to him and he said using his on the 833 would only involve making a different mounting bracket and the correct length drawbar. It's doable but spendy.
 
parshal said:
Regarding a power drawbar setup, I found Priest Tools which makes things specifically for PM and LMS mills. I talked to him and he said using his on the 833 would only involve making a different mounting bracket and the correct length drawbar. It's doable but spendy.
Click to expand...
Yeah. I designed and built my own power draw bar for the 835 (and previously for my Seig mill). It uses twin pneumatic cylinders to lift the ratchet and linear shafts and bearings to guide it. I made it difficult for myself since the draw bar drops by 5" when fully extended and I wanted the power draw bar to operate throughout the range. It didn't cost much and it works pretty well (as well as an HF butterfly wrench can manage). I think others have done the same but I don't know if they operate over the full 5" travel.
For machines with a draw bar that does not move up and down with the quill then building your own is easy and cheap, though some YouTube videos seem to make it unnecessarily complex.
 
davidpbest said:
Before you make a decision, don't discount the larger more advanced benchtop mills with their factory supplied base. READ the attached before you decide on a PM-935. If you'd like more information, let me know.
Click to expand...

David,

First many thanks for all your wonderful postings and documentation here and on the Felder Forum (FOG) over many years.

I just ordered a PM-833TV and in the process of validating what is actually on the machine I noticed one error in your comparison document - the belt drive on the PM-833TV has only one speed, also it is not BLDC motor but rather a 3 phase AC motor driven by a VFD. This was confirmed by Matt from Quality Machine Tools.

As I see it there is good and bad with this configuration.
The good:
Standard AC motor with probably standard mounting vs proprietary BLDC motor
AC VFD vs proprietary BLDC motor controller

The bad:
Lower low speed torque
No option for changing the belt gearing to get more torque in low speed

The area of advanced VFD is developing rapidly and there is a chance that in the future a better VFD, maybe with closed loop encoder will be able to replace the current VFD and get more low RPM torque. I don't have the machine yet so this is a speculation...

I am eager to hear your thoughts and other users experience with this machine.

Ariel
 
There is NO published documentation with specifics about the motor, electronics or belt drive on the PM-833TV. I put my head together with the guy who designs most of the VFD systems for PM equipment and we strategized that this system must have a 2-position belt drive to provide decent torque/HP at the extreme ends of the ranges, and we made the (apparently wrong) assumption about the motor and electronic drives. If Precision Matthews says it's a 3-phase motor with a VFD running it, who am I to argue and I will update my documentation. But first I want to see more specifics about the performance. There is no free lunch here.

This is why I'm skeptical: Assume for a moment the motor is 1000 RPM at 60HZ with a 1:1 spindle drive. Getting to 3000 RPM implies the motor is being driven at 180Hz, or three times it's normal frequency. To get to 50 RPM with that same configuration would imply the motor is driven at 3Hz (three Hertz). Here's that in spreadsheet form:

1000 RPM Motor at 60Hz.jpg


And here is a performance graph for 3-phase motors driven by VFD:

3-Phase Motor HP and Torque.jpg


Look at the likely power at 3Hz - something like 6 percent of rated HP. Maybe there is something I'm missing here, but looks to me like if the PM-833TV motor is being driven at 3-5Hz to get down to 50RPM, you're going to have the power of a Kitchen-Aid mixer.

I will be interested to hear how this 833TV configuration performs in real situations. For aluminum it's probably just fine. But my stock and trade is machining stainless and tool steel, and for that type application I would feel way more comfortable with the geared head version of the 833T, and possibly a 3-phase motor with a VFD to get up to higher speeds for aluminum. With the heavier geared head the machine is likely to have more rigidity, and six-speeds covers most of the typical workflow sequences like spot, drill, tap, chamfer. Minority opinion perhaps, but I did grow up in the Show Me state. :)
 
Hey Ariel, do you have the 833TV in your hands? I swear I'd seen something in the manual or somewhere else that it had a two pulley belt. Searching the manual now doesn't produce it. Mine is a few weeks away from delivery.

It machine more steel than aluminum. I initially wanted to the geared version but I was told the TV will work but just slower for that. Looking at David's graph I'm wondering now. I guess I'll see.
 
davidpbest said:
There is NO published documentation with specifics about the motor, electronics or belt drive on the PM-833TV. I put my head together with the guy who designs most of the VFD systems for PM equipment and we strategized that this system must have a 2-position belt drive to provide decent torque/HP at the extreme ends of the ranges, and we made the (apparently wrong) assumption about the motor and electronic drives. If Precision Matthews says it's a 3-phase motor with a VFD running it, who am I to argue and I will update my documentation. But first I want to see more specifics about the performance. There is no free lunch here.

This is why I'm skeptical: Assume for a moment the motor is 1000 RPM at 60HZ with a 1:1 spindle drive. Getting to 3000 RPM implies the motor is being driven at 180Hz, or three times it's normal frequency. To get to 50 RPM with that same configuration would imply the motor is driven at 3Hz (three Hertz). Here's that in spreadsheet form:

View attachment 314197

And here is a performance graph for 3-phase motors driven by VFD:

View attachment 314198

Look at the likely power at 3Hz - something like 6 percent of rated HP. Maybe there is something I'm missing here, but looks to me like if the PM-833TV motor is being driven at 3-5Hz to get down to 50RPM, you're going to have the power of a Kitchen-Aid mixer.

I will be interested to hear how this 833TV configuration performs in real situations. For aluminum it's probably just fine. But my stock and trade is machining stainless and tool steel, and for that type application I would feel way more comfortable with the geared head version of the 833T, and possibly a 3-phase motor with a VFD to get up to higher speeds for aluminum. With the heavier geared head the machine is likely to have more rigidity, and six-speeds covers most of the typical workflow sequences like spot, drill, tap, chamfer. Minority opinion perhaps, but I did grow up in the Show Me state. :)
Click to expand...

Wow, if this is the case it seems like an extreme oversight. I've come very close to buying this mill since it came out, and almost hope it is true so I stop it already.
 
parshal said:
Hey Ariel, do you have the 833TV in your hands? I swear I'd seen something in the manual or somewhere else that it had a two pulley belt. Searching the manual now doesn't produce it. Mine is a few weeks away from delivery.

It machine more steel than aluminum. I initially wanted to the geared version but I was told the TV will work but just slower for that. Looking at David's graph I'm wondering now. I guess I'll see.
Click to expand...
parshal, I don't have the PM-833TV on hand. I placed an order and realized that given the very wide speed range and the fact that it is NOT using a BLDC motor/controller the power available at low speeds will be very low for some of my demanding work at low speeds. For general usage it is probably OK and very convenient but given the lack of published experience I am looking at alternatives such as getting the PM-833T and replacing the single phase motor with a 3 phase motor and a VFD.

I am replacing a 35 years old RF-25 (Enco private label) that served me well over the years.

Any information on the topic will be appreciated.

Ariel
 
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