Bench Top Mill CNC Conversion (basic question)

For the money and time it will take to convert the pm 833 t I think you would be much better off going with a true cnc either of the used flavour or looking at some of the smaller cnc type machines from Novokon, Syil, Skyfire and Tormach. I think the Pm 833 t is a fantastic machine for what it is. It should be left as a manual machine for it s intended purpose. The gear head is a limiting factor in my opinion. Belt drive will give you years of service and much easier to maintain. Too much money wasted to bring the pm 833 t up to cnc standards. Unless you want a project and enjoy that I would skip it and spend the money on a ready made cnc. Will you really save money in the end?
 
MarkM said:
For the money and time it will take to convert the pm 833 t I think you would be much better off going with a true cnc either of the used flavour or looking at some of the smaller cnc type machines from Novokon, Syil, Skyfire and Tormach. I think the Pm 833 t is a fantastic machine for what it is. It should be left as a manual machine for it s intended purpose. The gear head is a limiting factor in my opinion. Belt drive will give you years of service and much easier to maintain. Too much money wasted to bring the pm 833 t up to cnc standards. Unless you want a project and enjoy that I would skip it and spend the money on a ready made cnc. Will you really save money in the end?
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I would agree the PM 833t is too expensive for the conversion. You would need the PM 833t, ballscrew conversion then the servo motors and electronics, etc.. Probably over $9000. Would suggest sitting down and working out the costs prior to making move. Then compare cost to a CNC mill already completed.

There is a website I found with one click that is going to offer a CNC conversion ballscrew kit for it though...
 
[QUOTE="bretthl, post: 654070, member: 48029"

I too noticed the 940 included stand weight. Not really a big deal but it is inconsistent in their comparison sheet.

I can afford a vertical CNC, I just don't have a place to put it right now besides the garage and that's not happening. Plenty of these out there for ~10K:

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My best guess based on the stand for the 940 being similar to the 932 is it is somewhere around 250 lbs.

I would love to referb an older VMC but as cjtoombs points out, getting 3-phase power makes it cost prohibitive, at least at my current location.
 
Cadillac STS said:
I would agree the PM 833t is too expensive for the conversion. You would need the PM 833t, ballscrew conversion then the servo motors and electronics, etc.. Probably over $9000. Would suggest sitting down and working out the costs prior to making move. Then compare cost to a CNC mill already completed.

There is a website I found with one click that is going to offer a CNC conversion ballscrew kit for it though...
Click to expand...

On my PM-932 conversion I have about $8,500 total into is including the mill, base, pneumatic drawbar, one-shot oiling system, coolant system, enclosure and 4th axis. About $700-$800 of that is for things I changed or upgraded over time.

I wouldn't pigeon hole myself into someone elses ballscrew kit. Design and specify the screws and mounts to fit your needs and constraints.

I agree on costing out the major components before deciding on what direction to go. Compare rolled screws vs ground screws, steppers vs servos, motion controllers etc.

Personally I design and build everything in CAD before ever ordering parts or cutting material.

I didn't build my CNC to save money, I built it for the experience and joy of building a machine. If I were trying to make a living off my CNC then I would have considered a commercial offering.
 
Get the PM.

Cheap, good:
Put a bigger 3-phase motor on it, direct, forget belts and gears.
VFDs don´t need any power, you can limit their draw via sw.
3-phase motors are almost free in power, as in 2-3-5 HP cost about the same in surplus center etc.

Since you mentioned You could buy a VMC, a servo motor on the spindle would be the right choice.
I have one on my 12x lathe, 2.5 kW cont.
1500€, +/-.
It´s about == to 10 HP industrial turning centers (Haas 11 kW 102 Nm max 1200 rpm, mine 90 Nm 0-1000 rpm).

A servo motor gets you 5-10x the torque and *surface finish* of anything else.
Yes it does - to my great surprise 3 years ago.
And rigid tapping.
And failsafe.
The servo stalls before breaking anything important, at 0.1 ms in time.

The acceleration of a servo is fantastic but useless, the top speed is mostly not important unless geared down like mine at 1:3.

There are zero realistic cnc mills comparable to a good servo refit.
A tormach new-model servo is probably the best, I think not yet available, around 20k$.
 
Well this discussion has been most helpful and a good reality check for me. I can see that a mill conversion would not meet my long term goals. I would not be able to attain precision from a low speed dovetail machine sufficient to justify the expenditure (time/money). It would be a fun project and enhance my understanding in general but down the road I would regret not going with a smaller industrial VMC. I will have to wait until the end of the summer when the stand alone shop is complete to have the space. Going with a used VMC scares the you know what out of me. I can inspect a manual mill or lathe with a high degree of confidence but I would be lost with a VMC. I have a hunch that most used VMC are for sale for a reason and that reason is not in my best interest.
 
Not necessarily! The smaller vmc s may have been a stepping stone and with a well documented maintenance program would give a fair bit of confidence knowing they went with something to improve the capability of the shop and just want the money from the machine they are selling.
 
In my mind it's just not worth the risk. Most likely the used machine will come from out of state. So unless I can find the time to travel and "inspect" (or hire an inspector) it will be sight unseen. There is a youtube channel called Full Throttle CNC and this guy lays out the process of buying a used machine. Rigging, transportation and setup alone can run 3K - 5K USD depending on the location. That coupled with no warranty or returns and the fact that used machines 20 years old command a pretty high price does not make sense in the long run. I would also need to consider availability and cost of replacement parts. He also speaks to the advantages of financing vs. paying cash outright (hard to finance a used machine) with respect to ease of future purchases. I'm not totally ruling out used but unless a local absolute deal appears it won't happen.
 
Just to confuse the issue a bit more, there is an intermediate step between a benchtop and VMC. The BP style CNC knee mills, available on the used market in several sizes from about 2500 to ~5000 LBS. Both in V and box way configurations, from 3 to 5 HP. I have 2 of these in my shop, one a 3V, and the other a 5V size. Both very capable machines and the 5V has a 24 tool changer. The downside is that they do not play well with flood coolant, in that it is difficult to contain.
 
I ll add more confuision along the same lines. Mitutoyo /Milstar retro kits are being sold with new Knee Mills. For the right candidate and the right timing for them. I think long term this would give the highest dollar for dollar value for three axis. It s for real right from the get go at an attainable price. Probably 1.5x what you might spend on a benchtop retro but then then you would not a want or need to upgrade to a Tormach or something. Thats s where you d see the value I think especially if you may work with it. Serviceability and support as well I would think.
 
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