LMS 3960 or G0704 mill for a small lab?

[TIGL]

Hey all. I just joined the forum because I'm about to dive headfirst into a project that's waaaaay more involved than than anything I've ever tried before and I know I'll have questions. I'm pretty mechanically inclined (even though I'm trained as a chemist) and my boss knows this so he goes and asks me to build whats basically a bench mounted robot with stepper controlled leadscrews and pneumatics (all automated). Anyway, I have a solid design mostly worked out and soon it will be time to build it. Only thing is that we don't have an in-house machine shop so we need to get at least a mill on top of the raw materials. I'm putting together a requisition to order a mill and for a while I'd been dead set on getting the solid column Little machine shop mill with the tooling package but the more I thought about it, the more I think it might be slightly undersized for what to do. I was looking around for similarly priced machines that I could put on the req as comparison quotes and stumbled on the G0704. Its about the same cost shipped and has no tooling but a larger table

Enough background, here's what I need to do: The core of this machine will be an 18"x18"x1/2" aluminum base-plate to which everything will be attached. In addition to the 1/4"-20 holes around the edge, I need to mill four 5/8" slots in a cruciform pattern around the center.

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This certainly seems like it would be pushing the little machine pretty hard but i think it should be doable. The center of the ends of the slots are 5" from the edge and according to LMS, the throat on the 3960 is 6.5". I'd probably need to drill some extra 7/16" holes so that I can use the clamping kit to bolt the plate to the table but it should be possible, at least dimensionally, to make the part. The maintenance department has a pretty beefy drill press so the peripheral holes and any clamping holes should be able to be made relatively easily on that. My main problem is the slots. According to Wolfram Alpha, the base will weigh just under 16 pounds which I imagine is a good bit less than the vice that will be mounted on the table most of the time. My main concern is the torque since about half of the plate will be cantilevered off the edge of the table which might put some unpleasant twisting stress on the gibs and ways.

Unless I get a strongly negative response from the HM brain trust, I'm still leaning towards the LMS mill for a few reasons. First, the next largest part I need to make is less than a third the size of the base and the rest of the smaller parts are smaller still. These smaller parts will demand precision that I'm not confident the grizzly machine has. Second, the lab space where this mill will go isn't that big so that the smaller footprint of the 3960 would be helpful. Not to mention the quieter operation in the lab and generally higher quality of the LMS option. Third is obviously cost. Having the machine and most of the needed tooling together (and as one line item) for under $1500 will make the approval process much faster and easier and I'm eager to get started on the project.

Edited to fix an error in the picture

 

[David Kirtley]

What you are showing is well within the cutting capabilities of the smaller machine (I have one down the hall - but the tilting version). It's a nice machine. I do think the G0704 is a lot more machine though. The additional capability of the tilt head does change the work envelope pretty radically.

 

[TIGL]

What you are showing is well within the cutting capabilities of the smaller machine (I have one down the hall - but the tilting version). It's a nice machine. I do think the G0704 is a lot more machine though. The additional capability of the tilt head does change the work envelope pretty radically.

Thats comforting. Do you find the fact that the handwheels have 62-1/2 divisions annoying? I tend to think in binary fractions these days so I kinda doubt having everything in sixteenths would phase me.

 

[David Kirtley]

Thats comforting. Do you find the fact that the handwheels have 62-1/2 divisions annoying? I tend to think in binary fractions these days so I kinda doubt having everything in sixteenths would phase me.

Not really, I don't use the divisions for more than depth of cut. I just set up a dial gauge if I have to but usually just am cutting to a line or center point.

If it is important, you can get the Micromark version with inch divisions or get the kit to swap out for inch or metric.

 

[TIGL]

Not really, I don't use the divisions for more than depth of cut. I just set up a dial gauge if I have to but usually just am cutting to a line or center point.

If it is important, you can get the Micromark version with inch divisions or get the kit to swap out for inch or metric.

Nah, I don't expect them to bother me, I just wanted to get someone else's first hand experience because it's a sort of unusual feature. It's a shame DROs are so expensive, I was spoiled by the bridgeport i learned on at school

 

[hman]

It's a shame DROs are so expensive, I was spoiled by the bridgeport i learned on at school

First off, hello from a fellow chemist (BS & MA, almost PhD) turned machinist/engineer/tinkerer!


Secondly, for a DRO you might want to check out http://www.hobby-machinist.com/showthread.php?t=21478&highlight=davidh

Davidh sells low cost iGaging DROs, which are not that hard to mount and have pretty good accuracy. I bought some for my lathe, and have been very satisfied. You can get X and Y for under $100, plus some of your time and some inexpensive materials to mount them.

See also http://www.hobby-machinist.com/showthread.php?t=10343 for one way to mount these on the mini-mill.


Thirdly, I have an HF mini-mill, and it's just fine to use, but does have some limitations I've run into from time to time. Chief among them is the distance between the column and the centerline of the spindle. At very best, I'm limited to about 5 3/4" from spindle centerline to workpiece edge. The LMS may be slightly larger than my HF, but be sure to check their dimensions! This limits how far "into" a workpiece you can go. You'll never get to the center of an 18" square workpiece with a mini, though your shorter slots might be do-able.

In addition, large workpieces require lots of relocation on that small a table, and you have to go through the (slightly laborious) alignment every time you move it.

Much as I love LMS and their products, of the two mills you're looking at, the G0704 is definitely more suitable for this project.

Best wishes!

 

[kd4gij]

If you wan't a dro the grizzly G0759 Is the G0704 with a 3 axes dro and only $500.00 MORE. i HAVE THE g0704 AND BEEN REAL HAPPY with it. Only wish Thay had the G0759 when I bought it.

 

[Ray C]

To some extent, the issue of the spindle only servicing the front part of the table can be remedied by using a proper size and style vise. A vise too large (which is a common mistake) puts the jaws in an awkward location. Some vises have center-location fixed jaws and some have rear-location fixed jaws. In some cases, the issue has more to do with the bolt-hole positioning and in such cases, an adapter can mitigate the issues.


Ray

First off, hello from a fellow chemist (BS & MA, almost PhD) turned machinist/engineer/tinkerer!


Secondly, for a DRO you might want to check out http://www.hobby-machinist.com/showthread.php?t=21478&highlight=davidh

Davidh sells low cost iGaging DROs, which are not that hard to mount and have pretty good accuracy. I bought some for my lathe, and have been very satisfied. You can get X and Y for under $100, plus some of your time and some inexpensive materials to mount them.

See also http://www.hobby-machinist.com/showthread.php?t=10343 for one way to mount these on the mini-mill.


Thirdly, I have an HF mini-mill, and it's just fine to use, but does have some limitations I've run into from time to time. Chief among them is the distance between the column and the centerline of the spindle. At very best, I'm limited to about 5 3/4" from spindle centerline to workpiece edge. The LMS may be slightly larger than my HF, but be sure to check their dimensions! This limits how far "into" a workpiece you can go. You'll never get to the center of an 18" square workpiece with a mini, though your shorter slots might be do-able.

In addition, large workpieces require lots of relocation on that small a table, and you have to go through the (slightly laborious) alignment every time you move it.

Much as I love LMS and their products, of the two mills you're looking at, the G0704 is definitely more suitable for this project.

Best wishes!

 

[SENC]

@wrmiller19 has both (actually the precision matthews version of the g0704), so hopefully he'll be along and can help you... but judging from his comments he has found the PM25 to be of higher quality than the LMS

 

[wrmiller]

Yes I have both, and like both machines for similar and different reasons.

The LMS is just as accurate as the G0704 if you use it as it was intended/within its designed to work envelope (I have the PM25 which is the G0704 with different paint, motor and controller). I consider the LMS one of the best, if not THE best mini-mill. Better motor, larger table, belt drive head, inch leadscrews, and EXCELLENT customer service from LMS. The 20 tpi leadscrews allow easier positional repeatability than the courser ones on the Griz. I have 3-axis glass scale dros on both machines and find it very easy to repeat position on the LMS to a couple tenths (observed on the DRO, verified on a dial indicator). The larger mill will as well, but a more delicate touch on the handwheels is needed.

I never used any end mill larger than a 3/8" rougher on the LMS because frankly, it doesn't have the mass/rigidity to handle anything larger without complaining loudly. I mostly used 1/4" end mills for aluminum, smaller for hardened steel like 1911 slides, titanium, and some of the more difficult stainless steels.

For small delicate work I give the nod to the LMS. Oh, and I highly recommend the air spring conversion from LMS if you get this mill. Positional repeatability increases dramatically on the z-axis with this mod. It also gives a bit more z-axis range. Always a good thing.

For larger cuts on larger work pieces and using larger end mills up to 1/2" I use the PM. I think of it as the LMS' bigger brother. More mass, more rigidity, more HP, larger table, etc., etc.. But it too must be used within it's designed work envelope. You try taking a full-width pass at a DOC of .5" with a 1" end mill in 4140 on this machine and you will likely at the very least shear the teeth off the plastic/nylon intermediate gear, or at the worst possibly damage your machine or tooling. I have milled everything from aluminum and iron to stainless and hardened steel and have yet to break the intermediate gear. But...I use small(er) cutters and modest cuts. This isn't a BP or Cinci. You need to take it easy and the machine will perform well and accurately.

The Griz/PM has tapered gibs which IMO make it easier to keep things tight and accurate. The gibs on the LMS work just fine, they just need a bit more fiddling to get things to my satisfaction. It (PM) also has a two-speed head that keeps the motor in a better torque range for slower rpm work if that is a consideration. I personally will be modifying the PM to a belt drive soon as I know better than to use large tools that require slow rpms on this machine, and the smaller cutters could benefit from a higher (3-4k) rpm operating range ceiling. (if after doing your base plate you find yourself doing most small delicate work, LMS has a belt drive/bearing upgrade for their mill that doubles the max rpm available)

That's pretty much all I can think of at the moment. If you think of specific questions, feel free to post 'em here or PM me and I'll answer as best as I can.

Bill