Time to add a mill. Knee or vertical?

RandyWilson

RandyWilson

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I've been wanting a mill. I got a lathe 6 months ago, now I really want a mill. I have identified an operation in my home business that I could do with a mill that is currently costing me $150 per unit at the local machine works. While that is so low volume that it will take many years to recoop the costs, it's enough rationalization; I'm gonna get me a mill.

My work space is limited. With the work I want to do, and the space I have, I identified the RF-45 type machines as a good target. But then I got a lead on a "used" Taiwanese 8x30 knee mill somewhat local. I got a look at it today. While it is 15 years old, they claim it has less than two hours runtime. And it looks it. The belts haven't even polished the paint off of the pulleys. The only mark I could find on the machine was a coffee cup ring on the table. The included tooling was in like new shape.

I am not looking for a Taiwan vs China discussion. Nor brand X vs brand Y. Or even Asian versus Merican iron. I've already read thousands of those posts. What I'm trying to decide is if the knee mill is worth the extra bucks. While I am a master at frugality, there is no equipment more expensive than that which won't do the intended job. What I can not find in all my searching is a good feel for the advantages and disadvantages of the two type of mills.

Reference machines,

http://www.grizzly.com/products/8-x-30-Vertical-Mill/G0730

http://www.machinetoolonline.com/PM-932M.html

Target usage is modifying aluminum transmission cases, other one-off automotive doodads, and random home-hobby puttering.


Any thoughts?


TiA

Randy
 
I was also debating mill/drill with round column vs a knee mill. The round column mill/drills came up more often on Craigs List. A few weeks ago a Grizzly G1008 knee mill appeared on Craigs List. Likely an older version of your G0730 link.

I was aware the mill/drill machines are not able to keep Z axis alignment when the head needs to move.

I am happy to have the G1008 knee mill. I have only had this machine for a few weeks, but already have appreciated the Z axis staying in alignment when I have needed to move the table. The spindle travel is 3 3/8in. I am a hobbyist woodworker and recently metalworker. I have used the G1008 to drill the holes in pepper mill blanks. I need to drill an 8+ in deep hole. I can do this on the wood lathe, but have experienced some drift in the hole. I was able to drill on the G1008 to the depth of the Forstner bit, then lower the table so I could add an extension to the Forstner bit then continue the rest of the way.

This may not be your intended use of a knee mill, but I think you would prefer a machine to maintain Z axis with vertical movements rather than one which does not.
 
The Grizzly G0730 you linked to is fairly light for a knee mill. You have not told us the real nature of the work you will be doing on your future machine. Could you give us some better ideas of what you will be planning to use it for? Modifying transmission cases can be a big job or a small and light job. A lot of good work can be done on very light milling machines, but heavy cuts and large parts can be problems. Even full size Bridgeport mills are considered to be "light" mills in industry, and sometimes derided as fancy drill presses. We hobbyists know better, but you are thinking about commercial usage.
 
RandyWilson said:
I've been wanting a mill. I got a lathe 6 months ago, now I really want a mill. I have identified an operation in my home business that I could do with a mill that is currently costing me $150 per unit at the local machine works. While that is so low volume that it will take many years to recoop the costs, it's enough rationalization; I'm gonna get me a mill.

My work space is limited. With the work I want to do, and the space I have, I identified the RF-45 type machines as a good target. But then I got a lead on a "used" Taiwanese 8x30 knee mill somewhat local. I got a look at it today. While it is 15 years old, they claim it has less than two hours runtime. And it looks it. The belts haven't even polished the paint off of the pulleys. The only mark I could find on the machine was a coffee cup ring on the table. The included tooling was in like new shape.

I am not looking for a Taiwan vs China discussion. Nor brand X vs brand Y. Or even Asian versus Merican iron. I've already read thousands of those posts. What I'm trying to decide is if the knee mill is worth the extra bucks. While I am a master at frugality, there is no equipment more expensive than that which won't do the intended job. What I can not find in all my searching is a good feel for the advantages and disadvantages of the two type of mills.

Reference machines,

http://www.grizzly.com/products/8-x-30-Vertical-Mill/G0730

http://www.machinetoolonline.com/PM-932M.html

Target usage is modifying aluminum transmission cases, other one-off automotive doodads, and random home-hobby puttering.


Any thoughts?


TiA

Randy
Click to expand...
It looks like to me the knee mill you will be able to tilt the head and swivel it . And move in and out on the ram making it more versatile.
Then the table mill . The head only move up and down and swivels 90 degrees
 
Thanks.

I should have mentioned that I do have a fairly stout floor drill press, so a round column mill/drill is not in consideration.

This would not be a commercial production operation; maybe 10 units a year.The first order of business would be boring two `3/4" holes through a boss that can have placement tolerances of +/- 0.050. The only critical part would be cutting an internal retaining ring groove. Other than that one step, I could do it with the drill press. A hand drill, even. I can also foresee in the future reboring bearing pockets for pressed in repair sleeves. The question isn't whether I should get a clapped out monster BP. I am confident the RF45 will do what I need. The question is why the small knee mill would be worth the extra coin.
 
RandyWilson said:
Thanks.

I should have mentioned that I do have a fairly stout floor drill press, so a round column mill/drill is not in consideration.

This would not be a commercial production operation; maybe 10 units a year.The first order of business would be boring two `3/4" holes through a boss that can have placement tolerances of +/- 0.050. The only critical part would be cutting an internal retaining ring groove. Other than that one step, I could do it with the drill press. A hand drill, even. I can also foresee in the future reboring bearing pockets for pressed in repair sleeves. The question isn't whether I should get a clapped out monster BP. I am confident the RF45 will do what I need. The question is why the small knee mill would be worth the extra coin.
Click to expand...
Versatility
 
Working distance between the spindle and the table will likely be larger on any knee mill. I have found that to be pretty handy on my Rockwell 21-100 to get work down out of the way of the head to take measurements etc..
 
I have a PM45M-PDF, the predecessor to the PM932. While I'm happy with it & haven't out grown it yet I've always wanted a full size BP style knee mill or even a 2/3 size. But I couldn't afford one at the time & I certainly don't have the room for one. I would have really liked a PM935 but they didn't come out yet when I bought my mill.

The RF45 style is ok for what I do but I would recommend a BP style knee mill if you can swing it & have the room. Hopefully someday I will have one but I'm not counting on it.
 
I had it in my head that the G0801 was a larger mill than something like the PM932 or the Grizzly variant the G0761. So I a graph and where I could compare specs between the two mills. The G0761 has quit a bit larger table, larger max distance spindle to table, more horsepower, comes with powerfeed, and more. You might do the same with mills that attract your attention. Also the G0761 is cheaper than the G0801 and a lot cheaper than the G0730. I still don't own a mill yet, but have been doing lots of research as you probably have. Hope my notes make sense.

Untitled by redmech, on Flickr

Untitled by redmech, on Flickr
 
I'm not looking to compare the two specific machines. I am looking for comparisons of the two types, Knee mill vs dovetail column vertical mill. I just don't see the big difference between moving the head up or the work down if they are both on dovetails. So far the only things I've found is a knee mill has gravity working for you rather than against when dealing with backlash but it is harder to install a DRO. There has to be something else to justify the 50% higher price.
 
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