# Square Column Bench Top Or Knee Mill ?



## GarageWrench (Apr 29, 2015)

Looking for some input:

I will be purchasing a mill for my home shop. I rebuild Harley engines and build custom motorcycles. I have a Rongfu type round column mill/drill w/dro and its time for a upgrade. To compliment my mill I also have a Craftsman 101 12x36 lathe. I would love to expand my machining capabilities and maybe even venture out and expand my (very small) operation and take on some job work. 

Its difficult to determine if a square column bench top will be all I need, and not need to upgrade in the near future. Need to make my hard earned money work for me, HD truck mechanic by trade and no extra funds to flush down the toilet. I have read just about all I can on this forum (which is awesome by the way) and else where, and I really do not want to purchase a used BP style mill and take the time to rebuild/work on. Time is money, and I know a new mill is my best choice. I have narrowed it down to the PM or Grizzly bench top or the Grizzly G0730 type mill. For what I do and want to expand into I am thinking the smaller knee mill may be best for me. I really need to be frugal with my money and my shop is really packed full, but I can make the room for a knee. 

I really enjoy reading all the post here, just looking for some input from all the experience that is here and help me with this decision. 

Danny GarageWrench


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## Pat of TN (Apr 29, 2015)

All I have ever heard is, a knee mill of just about any fashion is superior to a mill-drill, square or round column. And that is true. Knee-style mills are more common in industry. If I had my pick, I'd have a knee mill - I've just not got the space for one.


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## tmarks11 (Apr 29, 2015)

Knee mill is far superior to a square column mill.  Someone on this website just bought an 8x30, IIRC.  I think this is a good choice; reasonable price, made in Taiwan.

I have its grandfather, a Clausing 8520.


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## GarageWrench (Apr 29, 2015)

Tim, Not familiar with that name, IIRC, where do I find info on that mill?


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## tmarks11 (Apr 29, 2015)

Clausing is a famous name in machine tools.  The mill I have was built in the 60's.  You can find them on craigslist occasionally for $1000-2000. Well liked by hobbyists, but like any used equipment, usually requires some care and feeding. The 6x26 and 8x30 mills were patterned after it. The Grizzly 8x30 looks like a reasonable copy that should serve you well, and is a much better choice than the smaller 6x26 mills.

Again, knee mills are much more flexible and easier to achieve precision results with than a column, IMHO.

EDIT: never mind, just caught your question.  IIRC = If I recall Correctly.    The gentleman in question just bought the mill (Grizzly G0730) we are talking about.  You can read his thread and see his pictures here:

http://www.hobby-machinist.com/thre...ed-and-expecting-delivery-friday.34883/page-2


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## wrmiller (Apr 29, 2015)

That little 8x30 may not be large enough if you are going to be machining cases or heads. You really need to base your decision on the size and type of work you are wanting to do. I recently visited a gentleman that has an older 8x30 type and it is in no way more capable than my larger bed mill. Now if you think you need a tilting/nodding head, then a BP type could be a choice but the little 8x30 head doesn't nod. At least the one from Griz doesn't. But the PM935 does if you can swing that. But then again cutting angles is what tilt-tables are good for. Any given machining problem has more than one solution.

Opinions here are as varied as there are stars in the night sky.  To get some useful information on this you could help focus this discussion by describing the size and type of work you want to do, and maybe what you'd like to do in the future. Are you going to keep the 12x36 or are you going to upgrade that too? Having machines of similar capacities can be helpful.


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## tmarks11 (Apr 29, 2015)

wrmiller19 said:


> That little 8x30 may not be large enough if you are going to be machining cases or heads.



Good advice.  One advantage of square column mills is they are significantly cheaper than knee mills, so if you are on a budget, and need to mill something large, than they could be the way to go.  

The largest of the square column mills is the one sold by Charter Oak.  Coolidge will be alone any moment to chime in on this, as he just bought one.  

You can catch his posts about it on the Charter Oak forum.


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## coolidge (Apr 29, 2015)

What Bill said, start with the minimum work cube X x Y x Z that you expect to need. I recommend you cross bench type mills off your list round, square, or otherwise. Go knee mill or for Seal Team 6 level bravado find a used Bed Mill. Used knee mills should be on the table given you want to keep the cost down, if you have time, months to wait for a sweet one to surface and the cash to pounce that would help. DO NOT assume just because you purchase a new mill that you won't have to fix a bunch of crap.


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## wrmiller (Apr 30, 2015)

tmarks11 said:


> Good advice.  One advantage of square column mills is they are significantly cheaper than knee mills, so if you are on a budget, and need to mill something large, than they could be the way to go.
> 
> The largest of the square column mills is the one sold by Charter Oak.  Coolidge will be alone any moment to chime in on this, as he just bought one.
> 
> You can catch his posts about it on the Charter Oak forum.



Yea, my 12Z is what I was referring to.


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## GarageWrench (Apr 30, 2015)

wrmiller19 said:


> That little 8x30 may not be large enough if you are going to be machining cases or heads. You really need to base your decision on the size and type of work you are wanting to do.[/QUOTE
> 
> Yes, I have the means to weld cases and heads, but always need to send out for machine work. It's not the Z or X that is short it's the Y axis on the square column mills that seems to be a little short, most at less than 8". Like someone mentioned, yes I do have a budget and that style mill is much cheaper than a knee with the exception of the knee without the nod function, I guess there will always be that one area where your mill falls short when yer on a budget.


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## GarageWrench (Apr 30, 2015)

Ya still getting the just of posting here, forgive me for typing in the copy/paste portion of my post.


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## wrmiller (Apr 30, 2015)

The limited Y axis travel is why I ended up with a 12Z mill. basically a 10x40 table (rounding up .5") and I can get the spindle all the way from the back of the table to two inches off the front or more. And 20" plus of Z which is handy for doing larger stuff. I had a budget as well, but mostly didn't want a machine that I can't move myself because it's too blinkin heavy. The smaller knee mill wasn't too heavy, it just didn't have the Y axis travel I wanted and the table is a bit small. Always tradeoffs when compromising...

If the money and weight wasn't an issue I'd have a 9x49 BP clone with electronic speed control.  But for now this mill does everything I need of it. Biggest cut I've done so far is a 1/2" rougher end mill at 1" DOC full width. Worked fine. A little hard on the cutter though, as I don't have a coolant system yet.


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## GA Gyro (Apr 30, 2015)

Interesting dilemma... what machine to get... we all have been there.  
IMO the advise of determining the cube size of work you will do (X - Y - Z) would be something to consider; both current work and expanding into future needs.  

My vote would be to forget the bed mills and go with a knee mill.  I was ready to ask Matt at QMT (Quality Machine Tools, the Precision Matthews machines) to send me a PM932PDF (basically a clone of an RF45)... then at the last minute changed my mind and asked Matt to send me a PM935 (clone of a BP J head).  This BP clone cones in two sizes; a 935 or a 949... both have the same 3HP head.  The 935 is a bit lighter machine, generally called a 2/3 (or 3/4) BP clone.  The 949 is mostly a full sized BP.  The advantage of the 935 is weight (around 1600# vs around 2500#), the advantage of the 949 is the machine is more ridged- the ability to take serious roughing cuts.  Having said that, I have taken cuts with my 935 that will cause the motor to grunt, so one should not consider the 935 a light-weight by any means.  

If it were me, and the space/money were available, I would seriously consider the PM935:
http://www.machinetoolonline.com/PM-935HighPrecisionMills.html

Personally, I bought a 3PH motor belt drive (PM935TS) and put a VFD on it (VFD is a phase inverter, varies the phase to vary speed-- also allows you to run the 3PH motor with single phase current supplied).  I am quite happy with my choice.  

Lots of folks at this forum have purchase the PM935 series (both TS and TV).  With a little searching, you can find many threads of receiving, set up, and impressions of using the machine.  

On a side note, lots of those folks that purchased the PM935 also purchased the PM1340GT lathe... the two seem to be a good pair.  Again, lots of reviews on this lathe at this forum.


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## tmarks11 (Apr 30, 2015)

wrmiller19 said:


> Yea, my 12Z is what I was referring to.



Whoops, forgot to mention Bill got one too. 

Coolidge just sticks in my mind more, since he had to get two..


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## GarageWrench (Apr 30, 2015)

Ya Gyro, I would love to have that PM935, that would eliminate my budget, but I would get the XY and Z to cover all I would need and the ragidaty of the bigger mill. The Grizzly 9901 is also comparable.

I noticed the specs are very similar on the Charter Oak 12 Z and the PM 940m, the Y on both are 12". I don't think PM has shipped that mill as of yet.

In any ones opinion, how important is the auto down feed option on the quill ? Seems as a hobby machinists I could live without that. My mill/drill and lathe are both manual so that's something I'm used to, but I installed a DRO on the Rongfu and would love to have a 3 axis on the new mill (or used mill).

I'm thinking there is a significant loss of ragidaty from the square column to the knee, even the smaller knee's like the Grizzly  G0730 style. 

Thanks for all the input fellas, great info!


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## GA Gyro (Apr 30, 2015)

Matt's new PM940 is supposed to be in sometime in May... however it seems the freight never gets there on time.  

I may have a need for a CNC mill in the future... If I do... I am seriously considering the 940.  

And yes, I understand about the $$$ thing.  Many of us have joked about totally blowing our budgets (myself included)... yet when we have the machine, we realize it was a wise decision. Note I am not saying to get careless with $$$, just to not be too tight.  Future needs seem to always grow into larger machines... just the nature of the beast.


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## tmarks11 (Apr 30, 2015)

GarageWrench said:


> In any ones opinion, how important is the auto down feed option on the quill ? Seems as a hobby machinists I could live without that.


I am not a big fan of auto-downfeed.  I have used it on bridgeport for boring holes.  The advantage is that you get a better finish quality using the auto down feed.  The BIG disadvantage is the release mechanism that stops the down feed isn't real accurate, so you don't end up with the hole consistently at the depth you want it.  Not a big deal if 0.020" is acceptable error.  A real big deal if you want to get within 0.005".

I definitely wouldn't pay $300 for this option, unless it is much more accurate than the way that Bridgeport implemented it on their knee mills.  And even then, I wouldn't pay $300 for it.

Based upon other's experience with the Charter Oak, I would recommend investigating the PM940 instead.  Matt has a good rep on this board (and elsewhere).


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## JimDawson (Apr 30, 2015)

tmarks11 said:


> The BIG disadvantage is the release mechanism that stops the down feed isn't real accurate, so you don't end up with the hole consistently at the depth you want it




The trick is to finish the pass manually by pulling the quill down against the hard stop as the feed disengages.  It will normally hold better than 0.001.

.


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## wrmiller (Apr 30, 2015)

GarageWrench said:


> Ya Gyro, I would love to have that PM935, that would eliminate my budget, but I would get the XY and Z to cover all I would need and the ragidaty of the bigger mill. The Grizzly 9901 is also comparable.
> 
> I noticed the specs are very similar on the Charter Oak 12 Z and the PM 940m, the Y on both are 12". I don't think PM has shipped that mill as of yet.
> 
> ...



BP type knee mills are used by smaller shops because they are more 'configurable' with all the tilt and nod capability. Larger shops/factories  use 6 and 8 thousand pound (or bigger) Cinci and other brands of bed mills to do any serious stock removal in a production environment. I was talking to a tool and die maker of long experience one day and he described BPs as 'nice hobby machines'. 

But we're talking here about hobby use right? 

IMO the 935 is one of the highest quality knee mills available in a 3/4 size, but it is a bit spendy for some folks (me included). Matt's new bed mill (PM940) is near identical to my Charter Oak 12Z and if Matt had offered the darn thing when I was shopping I would have bought his instead of the CO just because I have already done business with him and have nothing to say but great things about it (well, other than the waiting around for the machines...but that's NOT Matt's fault). I personally am glad I didn't spend the money on Griz's 695. I think it would have been a great machine, but not quite up to doing some of the things the 12Z can do.

Does Matt have any idea when the new 940s are going to show up? When last I talked to him I was giving him some grief (good naturedly of course) about bringing in all these cool new toys AFTER I go and spend my money on something else.


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## tmarks11 (Apr 30, 2015)

JimDawson said:


> The trick is to finish the pass manually by pulling the quill down against the hard stop as the feed disengages.  It will normally hold better than 0.001.


The machines I have used (Sharp 1054, brand new) had about 0.010"+ flex in the hard stop.  Impossible to get an accurate cut with the quill. Maybe not the norm, but it was the norm on every machine in the shop.


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## wrljet (May 5, 2015)

In my limited experience with the small mills, such as Grizzly G0704, you don't have good control of the
down feed of the quill.  And no hard stop.   You can't lower the head on the column very carefully
to get an accurate depth change, because of stiction in the ways.  It's hard to move a cutter
down a known amount.  You measure something and know you want to take off .003" more.
Now what do you do?

With a knee mill like the Bridgeport you can raise the knee, carefully and against gravity while
watching an indicator, to get an accurate change in cut.

And the working envelope is just so small on the smaller mills.

Bill


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## xman_charl (May 27, 2015)

Use this magnet/1 inch dial indicator. Channel is from an old bedframe.


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## wrmiller (May 27, 2015)

wrljet said:


> You measure something and know you want to take off .003" more.
> Now what do you do?Bill



That's easy. On these types of mills (and what I do on my mills), you simply move the cutter off the workpiece, lower the head to something below your target depth then raise it to your target depth and lock the head. That way the head is always loaded by gravity against the leadscrew. I was talking to the owner of QMT about this one day on the phone and he says that on these machines he does the same thing. 

I have had to take .0006 off the head of a screw on my PM-25 using this method and did it perfectly without touching the material the screw was in. 

But this example is for side cutting only. Given the same scenario above for a pocket cut requires that you use the quill on these machines, and I simply keep a slight drag on the quill lock as I'm plunging to keep the quill 'loaded' against the gear. The digital scale tells me exactly how far I've moved. Lock and continue cutting.


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## Rex Walters (Jun 11, 2015)

wrmiller19 said:


> ... simply move the cutter off the workpiece, lower the head to something below your target depth then raise it to your target depth and lock the head. That way the head is always loaded by gravity against the leadscrew.



I'm curious: do you have a graduated dial on the Z-axis crank on your bench top mills? Or have you installed a DRO  for the Z-axis? My Grizzly G0762 doesn't have a dial for the Z-axis crank, but I'm considering manufacturing something. I only crank the head to get close, and use the crank on my quill (with a graduated dial) to mill to specific depths. I use a DRO for X and Y.

If you added a dial to Z, please share your design! 
-- 
Rex


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## wrmiller (Jun 11, 2015)

Sorry Rex, didn't design a dial. I have a 3-axis DRO on both of my bench mills. I use a separate digital scale on my the quill for plunge/pocket cuts.


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## zmotorsports (Jun 11, 2015)

I am one of the forum members who have purchased the PM935TV and love it.  I had originally ordered a benchtop PM932PDF but just couldn't wrap my head around the fact that it was a benchtop and Chinese at that.  I don't mean any offense, I am just anal about my tools and wanted a higher quality machine.  I blew my budget to hell and ended up with the PM1340GT lathe and the PM935TV mill.  I have owned them for about a year now and fall in love with them all over again every time I use them, which is several times a week.  The fit & finish is excellent and they run smooth and true. 

The PM935TV uses a full featured Bridgeport head, is  a BP clone in a 2/3 body.  I fabricated as riser/base for mine to get it up about 8" higher than sitting on the floor and it is perfect for my 6'2" height. 

I would follow others recommendations to base your decision on your work envelope and take a good look at what you routinely work on.  I do a lot with motorsports, mostly motorcycles any more but lately have turned into a bit of a general job shop with these new machines.

Mike.


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## Falcon67 (Jun 22, 2015)

I love my G0519 - but I'd sale it in a minute for a good 9x? knee mill.  The square column does many things well.  It's fairly accurate but it could use some help.  Not even close to the usual specs you see for a Meehanite casting based knee unit.  I could hold .005 with care on things and that is pretty good for most work.  A 2nd 4" vice will be here today and I'm saving up for a 3 axis DRO.    The DRO will make some things easier.

That said, there are some things I'd like to do - possible performance cylinder head work.  For that, the square column is there in HP but not even close in tolerance.  if I could find a good accurate 9x49 around $6K, I'd be 2/3rds of the way there.  Minimum tooling will be in the $3000 range.  Don't have the $ right now so just have to wait - had to invest $7K in the house AC this year, so maybe 3-4 years from now.    Not many mills crop up around here so there is at least a 80% chance it would be a new purchase.  The Enco Turn Pro model was in that price range with the last 30% off+web sale but I picked the 12x36 lathe because we just could not go that much on the mill.  Since the AC had to be replaced this year, must have been a premonition LOL. 

So it really goes to what you want to do with the tool.  Knee mills are much more flexible, especially with the tilt and nod capability.


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