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View Full Version : IH vs Knee Mill



SCzEngrgGroup
11-09-2007, 07:24 PM
I'm torn between an IH and a knee mill, either a used Brdigeport, or a new higher-end import like the Birmingham. My key requirements are a minimum 12" Y travel, and variable speed, since I will immediately CNC it.

So, the question is: What are the relative pros and cons of the two types of machine? If I buy an IH, will I later wish I'd bought the knee mill?

I'm going to ask the same question on the Bridgeport forum, so I get both sides of the argument.

Regards,
Ray L.

davo727
11-10-2007, 12:57 AM
Hi, One thing Ive heard from some that have CNCd knee mills is they are not happy with the performance of the Z axis when driving the knee. There is more weight to deal with and it ends up being really slow. The IH or rf45 style have a fairly heavy gearbox and motor assy but they still perform better cnc in the Z axis than the kneemills do. I dont have a knee mill or a IH mill but I have a RF45 style mill that I am converting which is like the smaller redheaded stepchild of the IH. ( Disclaimer- yes I know the IH is much bigger and better) I got my mill local pickup during the time IH was on hiatus and not available. Kneemills are pre world war2 design. The other one is cooler :) Dave

wildcat
11-10-2007, 01:03 AM
Used equipment has always worried me... my luck would be that by the time I got it used it would be in need of replacement. Buying a IH turn key certainly would have an appeal over CNC'ing a knee mill if my business relied on a CNC mill.

mcarvey
11-10-2007, 12:18 PM
I have a IH mill with the CNC kit but do not have a Bridgeport type mill. I have been using the mill for around two years. I am not using it in a production environment.

Pros of IH type mill (compared to a knee mill):
-Its much smaller and lighter which was important for me because I had to bring it down into a basement. The light weight makes certain elements of CNC'ing a mill easier if you have limited lifting help.
-It is [probably] much less of a hassle to set up for flood coolant. All you have to do is to make a basin on a table and put the mill on top of it. Adding some plastic sheeting to the sides of this does a great job of keeping the coolant from getting everywhere. Although I haven't personally added flood coolant to a Bridgeport type mill, I feel that making a catch basin for it would be much more of a hassle (although certainly not a deal breaker.) I'm sure those who have CNC'd knee mills can shed more light on this.
-You know exactly what condition the mill is in when you get it. You don't have to deal with any hassles of a used mill.
-Technical support is readily available from a company.
-Gearhead is nice if you are doing a job that requires switching back and forth between really low speed and high speed applications.

Cons of IH type mill (compared to a knee mill):
-Gearhead is [probably] not as quiet as a belt drive and [probably] has a lower top speed. If you add a VFD to the mill, the benefits of a gearhead become diluted. This is more of an annoyance than anything since I paid for a gearhead and rarely use the low speed gears. I'm sure that people who frequently use fly cutters have a different opinion. :)
-My 2.5 year old model IH mill is nowhere near as rigid as the Bridgeports I've used. Then again, the IH mill was a fifth the price of a new Bridgeport so I can't complain too much. It should be noted that I haven't used the newer version of the IH mills (I hear they are better) and have never used an import knee mill. For my applications the IH mill is plenty rigid enough for my applications.
-A Bridgeport or import knee mill probably has a higher resale value if you decide to sell it in a few years.

As with most things is probably depends on your applications, but I will say that aside from a few hiccup's (which I believe have been worked out in the newer versions) I have been happy with my decision to buy the IH mill with retrofit kit.

I hope this helps.

-Matt

IHCNC
11-14-2007, 04:47 AM
Thanks Matt for the compliments.
Our new head is actually quieter than our belt drive head. In the first 4 gears all you can hear is the VFD motor and fan at 4000 rpm. 5th gear makes a beautiful sound and in 6th gear at 3450 rpm you know you are humming. The new 12.5 IH Mill is 50% more rigid than your older IH Mill putting it right up there with a BP. As a Full Servo CNC Mill it's the biggest bang for the buck you can get.