Upgrading from 4" column mill to Knee Mill -- Looking for advice.

[slow-poke]

A while back I purchased an 80's style 4" column mill, added a VFD and converted it to CNC running under mach3 for hobby use. My idea at the time was just get a machine and learn enough to make some decent looking parts while learning the basics and hopefully by then be able to make a slightly more educated purchase of a more capable (and expensive) machine. Tons of fun to this point, and I'm now thinking about upgrading. My present mill works quite well, my only complaints being the loss of registration when cranking the head up and down and the ACME screw vs. ball screw limitations (although mach is pretty good at compensating for the backlash). I considered upgrading to ball screws but am now thinking start fresh with something more capable than a 6" machine.

This is what I have now after adding CNC capability (I have since added guards over the belts and gears):
I'm considering replacing it with something like a 8 x 30, something like this: https://www.busybeetools.com/products/knee-mill-vertical-craftex-cx-series-cx603.html
This appears to be be the same as a Grizzly G0731.

I would either remove all the CNC parts from my original and mate them to the new mill or sell my existing mill with all the CNC stuff included and just do a similar conversion on the new mill.

How do these 8 x 30 Clausing clones compare to a used Bridgeport or similar quality mill?

What other models should I consider?

I don't really have a feel for what price I should ask for my existing mill with all the CNC stuff included, any wild ideas as to what a reasonable asking price woule be?

 

[Dave Paine]

I have a Grizzly G1008 8x30 knee mill which looks to be the same design as the present model G0731. Mine was made in Taiwan in 1999. I purchased it from the original owner in January 2017.



I use the mill a lot for metal and wood projects. Tramming the head is a pain since no screws to adjust the tram, so the old nudge-and-fudge method.

Changing belt speeds was also a pain due to insufficient movement of the motor so hard to get one belt off. I finally removed the middle auxiliary pulley, flipped the pulley on the motor. I now have only 3 speeds but they are useful for my needs and changing the belt is now easy.



This style of mill does not have is a ram to move the head horizontally, or the ability to nod the head.

I have not needed to nod the head, but I have wished I had a ram when doing some operations on wood projects which tend to be bigger than metal projects.

This style of mill is also lighter than a Bridgeport, so light cuts, which you will know from your present mill.

A big benefit of this mill is the low height. This fits into my shop easier than a Bridgeport style.

The mill does not have power feed on the quill, which has not been an issue for me.

 

[tjb]

If feasible, you may wish to consider a BP or BP clone. On the plus side, all the constraints noted by Dave can be met. However, the challenges are size (as noted by Dave) and the likelihood of needing a 3-phase converter. Like you, I am purely a hobbyist but opted to start with a full size mill. I bought a used Supermax mill (full size, Taiwanese clone). Obviously, that made a 3-PH converter essential, but I have not regretted the decision. If you choose to go that route, I suggest you examine some of the H-M threads on 3-PH conversions. You don't want to make a mistake by under-powering. Mine is an American Rotary system, and it powers my mill and a lathe. ZERO complaints.

Regards,
Terry

P.S.: That's beautiful work on your CNC modification.

 

[Smithdoor]

Looks great
I would like one too no money and no space

Dave

 

[seanb]

You don't say where your at in Canada, but my vote is for a Bridgeport as well. keep an eye on craigslist and or its Canadian equivalent for a good deal. There are cnc conversions for the Bridgeport available. I think you will be disappointed with the grizzly mill and a new Grizzly will be as much or more than a used Bridgeport.

 

[Mjohnson]

I had one of those and did a CNC conversion. The quill was the Z. It had a 3 inch stroke I believe. It was OK, but I was never able to use tools in fixed holders and a tool table. I had to move and so I sold it.

If I were going to upgrade from a round column mill, I will look closer at the PM-30 from Precision Matthews. It's about 1/2 the price of that knee mill and has a similar work envelope. Unless you see a need to rotate the head and hang large odd shaped work off the side of the table. If you have to do that, then the knee type mill has an advantage.

 

[markba633csi]

Nice conversion, I'm sure it took lots of hours. I don't think you'd have any trouble finding a buyer, especially around Christmas time

 

[mattthemuppet2]

I have the smaller Grizzly equivalent - very sturdy for its size with a decent work envelope for my needs. However a square column bed mill is going to be way easier to CNC than a knee mill of any sort.

No idea on value, but CNC'd hobby mills never seem to get the money that owners want for them. I think that there's too much of a "risk premium" attached, plus a reasonable cost (say $2000 for yours) pushes it up into the "half decent larger machine" category. I'd take the stuff of the RF, put together a basic kit and sell it as a starter package, say $800-1000. Depends on where you are and local machine prices.

 

[slow-poke]

If feasible, you may wish to consider a BP or BP clone. On the plus side, all the constraints noted by Dave can be met. However, the challenges are size (as noted by Dave) and the likelihood of needing a 3-phase converter. Like you, I am purely a hobbyist but opted to start with a full size mill. I bought a used Supermax mill (full size, Taiwanese clone). Obviously, that made a 3-PH converter essential, but I have not regretted the decision. If you choose to go that route, I suggest you examine some of the H-M threads on 3-PH conversions. You don't want to make a mistake by under-powering. Mine is an American Rotary system, and it powers my mill and a lathe. ZERO complaints.

Regards,
Terry

P.S.: That's beautiful work on your CNC modification.

I have a 3-phase motor on my existing mill and use a VFD, will definitely do that again, the speed control and torque are great.

 

[Chipper5783]

Perhaps run through the usual list of constraints, such as: available space, available power, budget, transport, load/unload. Also, what is your intended use: work envelop, existing resources, planned projects. Obviously you are not new to this activity. Is it your ambition to do the CNC conversion, or do you want to take on the sort of projects that would really benefit from the capabilities of a CNC?

I just picked up a 20 year old industrial VMC. I think the cost & effort vs the capability is very favorable (Duh, if I didn't believe that I wouldn't have bought it). You can end up with competencies that a person probably would not build on a converted knee mill: ball screws, spindle drive interface, chip conveyor, full enclosure, flood coolant, very robust way covers, automated lube system, tool changer & air blast cleaning, air padded spindle seal, 4th axis, 40 tools . . . . and so on. Of course, you can walk into a store and buy all that and more most any day of the week - just consumes far more money than I was prepared to spend. However, at a a bit over $12K for a working machine that simply has a less efficient programming interface than a current machine, will provide a lot of capability that would be difficult to develop on a converted knee mill.

The base machine you linked in your first post will be half of what I spent, you'll spend additional time and money (and have a good time doing it) and end up with a pretty modest CNC. I am always very impressed by people who convert a machine they way you have. To me, it seems like an expensive (time and money) approach for the resulting capability.

Let us know how you make out.