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Thread: Knee Mills vs. Bench top Mills
09-03-2009, 07:07 PM #1
Knee Mills vs. Bench top Mills
I am interested in getting a milling machine. I have looked at a few used bridgeport knee mills and they seem to be well used. They are probably still good machines but not a nice as I would hope for considering the asking price.
Also I will have to rent a forklift to be able to unload a knee mill which is $300 so I started thinking maybe I should look for a new bench top mill. I cant afford a new knee mill but could probably swing a new benchtop mill. Everything I would ever want do I am sure I could handle in a bench top mill but it would be nice to have the spare capacity of a knee mill. So how do knee and benchtop mills compare?
What is a good brand of benchtop mill to look for? Would like to stay with american made machines if possible. The only thing I know to look for in a bench top mill is a square column, is there anything else?
thanks for any comments/suggestions
09-03-2009, 08:03 PM #2
have to raise the head on a round column machine. Such as if you had to raise
the head to put in a drillchuck or long drill bit. That is the only issue I have with them.
Somebody told me that there is a workaround but he didn't go into detail.
American made bench mill? Hmmm. I don't think there is one unless you go for one of the
hobby types like Unimat or Sherline (not sure of spelling).
Square column? Hmmm. I think the small hobby ones have square columns.
09-03-2009, 08:18 PM #3
Bag the idea of a benchtop. You are worried/inexperienced moving larger machines. Forget the Bridgeport...or have a rollback move it for you.
I think you would be best served looking for a Rockwell, or Clausing 8520/8530 vertical mill. They are not quite 1/2 the sz of a bridgeport. They have dovetail ways on all three axis. Can be diss-assembled and moved w/ an appliance hand truck that you could rent. A nice will be $2000-ish +/-
Slightly bigger at about 1500 lbs and about 1/2-2/3 the size of the bridgeport is a Burke or Powermatic millrite. Price will be $1000-$1500 +/-.
Search around, you will find more info on these machines. Prices are a guess and depend on the level of tooling they come with. With the bad economy, perhaps you might be able to make a better deal.
09-03-2009, 08:31 PM #4
for the grand total of $25 for one days use. The owner of the mill let me borrow
a 2 wheel skid to put under the base to move the mill into its new home.
Imagine a "[" piece of 1/2 inch steel lying flat with a wheel on each end.
[_______] . "" denotes the wheels. It's wide enough to fit under the base. Works great.
09-03-2009, 08:31 PM #5
I've managed to get by with a benchtop mill/drill for many years. It takes trickery and a certain degree of masochism. Any sane person would get a knee mill, even if it's one of the smaller ones. BTW, the vise is everything. I have a big Kurt CNC vise bolted to my mill/drill and it makes all the difference between being able to do quality work, and junk. I had an import vise and it just didn't cut it. My vise is worth more than the price of the mill/drill. Another area the mill/drill can't compete with a real mill is surface finish. It just isn't very rigid compared to the structure of a BP, and there's not much you can do about it. There are good BPs out there, along with Tree and various others. Hold out for a good example of the real thing.
09-03-2009, 08:38 PM #6
I would definitely pick up a used knee mill if I was able too, but the best type of benchtop mill you are going to find is a Rongfu RF 45 type mill with a box column. Along with having a box column they have a very large work area. Rongfu does make them, but Lathemasters makes a nice clone, along with other importers (aka, grizzly, enco, etc).
I went through a very similar choice a year ago and I ended up picking up a J-head Bridgeport for a killer price, could not be happier with it.
09-03-2009, 09:26 PM #7
Currently, Bridgeports tend to be under $1000 at auction in the Chicago area. The last sale I attended had 2 or 3 that did not get bids at $300, and were in usable shape. If you have the ability to inspect, you can do well.
If you are looking for a smaller machine, I second the Rockwell / Clausing idea.
Rong Fu square column is a respected machine, and worth the investment.
I am not a mill/drill fan due to the issues with losing adjustment when raising or lowering, and loss of rigidity when extending the quill.
More knee mill options:
Bridgeport Round Ram. They usually come with an M head, so you may struggle with tooling issues, but those are not insurmountable. The mill is smaller and less powerful than a V ram with J head, but still rigid and powerful for most home shop applications. A J head can be fitted with an adaptor, so the ability to add a more powerful head to a solid, but compact base exists. I have an M head RR, and like the combination of a serious mill in a small package.
Older horizontal/ vertical mills: I just sold a very nice Sheldon/Vernon horizontal mill. I was impressed with the rigidity and solid feel of this small machine. There are two types of Sheldon vertical heads that can be fitted to the machine, and many people also fitted a Bridgeport M head to the overarm. A package worth serious consideration for 30X30 inches of floor space for a light industrial grade machine. (you can see pics in my for sale post, and at Tony's: lathes.co.uk .) Hardinge also made a very similar horizontal/vertical machine.
I currently have a Benchmaster for sale. This machine can also be fitted with vertical head, and is a nice hobby size. Lighter than many other small mills, but still usable. If it was good enough for Rudy.....
Some comments on the Atlas vertical mill have been a bit disparaging. It is lighter than the Benchmaster, and suffers from some rigidity issues. They show up for sale, and have been used to make good parts. As long as you understand the limitations of the machine, you will be satisfied.
I generally like the older machines better, so that is my bias. If you can find a nice used machine a a good price, you can also sell it later and move up.
Regarding moving: I moved a v ram Bridgeport out of a Chicago basement with an engine hoist and furniture dolly. Just break it down to sub assemblies and take them out one at a time. The column was the toughest part. Roll it on pipes, or use a pallet jack. 2 guys can lay down or tip up a bare column without issues. Use some sense, and work safe. Besides, you'll need to disassemble and clean all the ways and lube channels anyway, so just tear it down, move it, clean it, reassemble and use it!
09-03-2009, 10:27 PM #8
Having lived with a round-column mill/drill for 8 years, I actually felt slightly guilty at selling it to a guy who wanted to learn machining as a hobby. They have so many shortcomings that they are very difficult to learn on.
As someone else on PM said "Anything with 'Bridge' and 'Port' in the name will cost you extra." It's true: B'port mills cost about $1k more here in the Bay Area than other brands of mill in similar condition.
09-03-2009, 10:31 PM #9
09-03-2009, 10:43 PM #10
But anyway the table was shorter than most, and it had deep scratches and nicks in every inch of it. Probably fairly accurate but thats the main reason I walked away from it. It had a newer x power feed and a very old DRO on it. They were asking $2600. Is that a fair price for one with the variable speed head?
09-03-2009, 10:50 PM #11
Could somebody please explain to me what the difference is between the M head and the J head? And the difference between the series 1 and series 2?
Also another machine I am looking at is a mid seventies machine with the bridgeport brand power feed. Does this machine have any bad traits? Some one was telling that the bridgeport power feed is very heavy and can bow the table over time. Is this true? I think it is a metal casing power feed but it really dont look that heavy. It has the mechanical kill switch.
09-03-2009, 10:52 PM #12
09-03-2009, 11:16 PM #13
If you are after a mill that is basically a small knee mill, I can only think of one option that would be available new from a store. I know this is probably worse than getting one of the smaller Clausings or Rockwells, but an easy to find option would be one of these: Grizzly G3102, or if your on a budget I dare say Harbor Freight (No. 40939) carries a red one . Remember do your research about the lack of quality and finish imports offer and see if you can deal with it.
09-04-2009, 02:03 AM #14
Bottom line is that if you intend to do any amount of 12" to the foot scale work anything smaller than a 42" table Bridgeport is too small and will involve you in endless work arounds during setting up or for tool clearances.
Pre Bridgeport I had a Chester supplied White Eagle ZX32 square column bench top. R8 taper version ('cos a Bridgeport was always in my future), two speed belt drive with VFD control ('cos the standard gearbox versions make a hell of a din right at ear level). Once the Chinee (un)QC issues had been sorted it was a decent machine quite capable of making cuts pretty much as large as I'd care to put on my Bridgeport. But the table was 27" by 8", maximum daylight under the spindle was 19", X travel 13", Y travel 8" with only 6" of table width accessible to the cutter. Hideously cramped once you start getting vices, work clamps, cutter holders and so on involved. Remember a decent vice is getting on for 4" deep, 6" if its on a swivel, a drill chuck or cutter holder getting on for 3" with cutters and drill projection lengths from 1" to 4". That lovely 19" daylight under the spindle is down to between about 7" and 10" in practice assuming you can get the spindle axis clear of the work for tool changing. Even less with a rotary table up. Clamping to the bed wins daylight but still needs about 4" each end to get the clamps in, on all but small work you can forget about clamping front and/or back. The tilting head is a great idea for angular work. Until you look at where the end of the cutter is in relation to the table. At any serious angle you have major mounting problems. Having to re-mount a tricky job multiple times is bad for the blood pressure. Not helped by the huge square head which is always in the way of seeing WTHIGO or getting measuring gear in.
Thing to remember is that tooling space and mounting issues are pretty much independent of machine size, more a factor of work scale so for modelling work with smaller components in smaller mounts its not so bad. Given this a Bridgeport looses about the same amount of space to mounts and so on but porportionally the gain in working space is much, much larger. Nominally around double the size in linear dimensions but the actual gain in working volume is at least 8 times not the 4 times you'd expect from the crude calculation.
I thing our perceptions of size are skewed by lathe experience where, for all practical purposes, the tooling goes outside the work envelope so capacity pretty much scales.
The Bridgeport price premium comes partly from the fact that everyone knows what they are and partly from the fact that being a common machine service stuff and advice expertise can easily be found. In the UK the big Beaver is considered a vastly better machine but you can't get parts so a fixer-upper or potential need for a big service down the line means they aren't viable for the HSM.
09-04-2009, 04:07 AM #15
This is the machine I have in my home shop. I have DRO, power X, an 8" tall 3/8" wall steel tube riser, and the best part is I adapted a vintage step pulley BP head onto it which gave me a back gear, Z feed, and quick reversing with the 3ph motor. It's a good machine and I use it a lot. Think of a 7/8 scale Bridgeport.
Of course I'd rather have a real BP or other industrial duty machine but in my home shop this Grizzly does a nice job. As far a benchtop goes I second the comments about round column losing center if you move it and lack of rigidity. I sold my benchtop to a buddy who uses it for smaller and lighter projects such as making guitars and he seems happy with it. It wasn't enough machine for me.
09-04-2009, 04:53 AM #16If you have a hole centered on a bench top mill you will lose alignment when you
have to raise the head on a round column machine.
09-04-2009, 05:08 AM #17
Bridgeport heads: short version
M head: 1HP, belt change for speeds, Tooling shanks up to 1/2 inch, Spindle taper: MT2, B&S 7 or the odd BP taper. (All hard, but not impossible to find. One supplier has new Asian collets and mill holders at reasonable prices.) This head can be found in 1ph mode!!!!
J1: 1-1/2 HP(I think), Belt change for speed. Tooling shanks a bit bigger (Not sure on largest size.), R8 spindle: much easier to find.
J2: up to 2 hp, dial up for speeds, R8, and maybe? NMTB tooling: much larger tool shanks.
I believe J heads also have power spindle feed.
However, size and weight increase with HP. The M head is appreciated because of ease with odd set ups, cursed when hogging material.
Table feed: Heard the same about bowing the table. Never had anyone prove it. Store with table full left, and it should be minimal issue. The drive is mechanical, easy to troubleshoot, about 100 lbs. Use it until you want to replace it with a servo.
Please correct me on the head info if necessary. I am really familiar with M head, less so with J.
09-04-2009, 07:49 AM #18
As a recovering Mill Drill user, I can state that if at all possible, hold out for a small knee mill. The point made above about losing your reference points (tram) when raising or lowering the head on a Mill Drill is quite important. It's discouraging to have to attempt to relocate a center or an edge simply to use a longer tool or change collets to a different end mill.
This point is something that I learned by reading and listening to the many posts here and elsewhere on this particular issue.
With regard to the cost of a forklift, you will only need it once. The machine you move in will be there for a long time if you are a typical user. Mill Drills are not particularly light, either. The one I had weighed around 700 pounds with the stand.
If space is at a premium, I would continue to look for a smaller knee mill, perhaps something American.
Just my opinion.
09-04-2009, 08:39 AM #19
M head machines are nice machines for modelmaking, etc. and I actually has one that ran on single phase 220VAC at one time years ago. Only disadvantage of the single phase machine is the spindle won't reverse instantly; makes power tapping rather exciting. [IMG]file:///C:/WINDOWS/TEMP/msoclip1/01/clip_image001.gif[/IMG] Biggest problem with finding an M head machine these days is they are all going to be elderly.
The larger machines with the 2J Varispeed head were always the most desirable, and would bring premium price. Unfortunately, the Varispeed drive requires more maintenance than all the rest of the machine combined. The heads get noisy but continue to run; continued operation can screw up a lot of rather expensive parts, like the movable pulleys and motor shaft. All the 2J heads came with three phase motors.
If I were buying a B'port for a home shop, I'd look for one with the step pulley J head, and plan on using a VFR (Variable Frequency Drive) to power it rather than a phase converter. The VFD allows finger-top control of the spindle speed, so the belt can just be left in the mid range, but the belt can still be changed to the lowest range for those jobs that require max. torque. VFD's rated 3HP and less that run on single phase 240V are easy to find, and only cost a couple hundred bucks.
09-04-2009, 08:49 AM #20
BillTodd -- that's a very clever solution. How repeatable was it?
I had considered building a "second column" at the rear of the machine, but decided that I'd rather spend my time earning money so I could buy a bigger, better machine.
Also, I'd put in a good word for Taiwanese machines - they cost more than similar mainland Chinese machines, but the design and quality control is generally far superior. These seem to occupy a "sweet spot" of good price/performance value.