Which CNC mill to buy? - Newbie question

[chns]

Probably been posted a million times before, but without any serious background in the area I'm getting very very lost trying to figure out what I need to buy to get started. I'm mostly looking to mill aluminum. CNC software/hardware doesn't need to be too fancy, just looking to do the basics in 3 axis with an acceptable degree of precision. The big problem I'm having is that threading is a must (non-standard threads, large diameter, etc.), so I figured a CNC rotary table is a basic requirement, but I'm having trouble finding resources on how exactly I can thread with a mill and what components I need to buy to do it via CNC (is helical interpolation something I achieve mostly via software or hardware? What type of tool/setup is used for the task?)

The other problem is my ideal budget is $2-3k for the whole setup, and space/portability is an issue - I will have to deal with the cons of a smaller, lighter setup. I'm quickly realizing that's unrealistic and I'll probably have to shell out more to get a decent setup once I account for the mill, CNC conversion (or a CNC ready mill), steppers?, controllers, software, etc.

My only advantage is I have an X2 mill (I think its an X2 but I may be confused. Its a G8689 from grizzly) and a spare computer to use. Dunno if the best option would be to retrofit my mill for CNC or start from scratch though. I've been looking at the sherline CNC mill that gets you a ready-to-go setup (even includes a computer) for ~$2.5k, but it seems pretty dang lightweight: I already have issues with not enough clearance on the X2 between a chuck and a vice, so I doubt the sherline would suffice.

That said, any advice? I'm very lost amongst a sea of mills, CNC choices, hardware and software options, and then I have my own ignorance on top to complicate things. So thanks in advance for any help you guys can offer!

[sansbury]

That is indeed an X2.

What you are probably looking for is called "thread milling" and if you search that you'll find a lot more info. It is done solely with XYZ moves (with helical movement) and a thread milling cutter which you can find from the usual major suppliers like MSC, etc. The programming is not terribly complicated and doesn't necessarily require any software at all. It can be used to mill internal or external threads. It's probably not something to do on a sloppy machine as it depends on the ability of the tool to make fairly round movements.

The X2 is a common project machine here--I'm about 2/3 of the way through one myself. With a mill and PC already available you can probably do a conversion for $1000 or so depending on how you go about it, whether you buy a kit like KDN Tools or CNCFusion, or go the DIY route like Hoss. I'm doing the 100% DIY approach and it is basically a gremlin around every corner, but you learn something with each one you kill, and so far I am seeing the anticipated savings of around $300. I won't say I've enjoyed every minute of it but I approach each major component as a test and I am happy as I pass them as they have forced me to stretch my abilities in various ways. A kit would not do this nearly as much.

The best alternative IMHO is a Taig, which is a good quality US-made tool like the Sherline, but a bit more metal in some important places, and therefore suitable for larger work, and only a bit more money. If you are in a well-populated area you could probably sell the X2 for $400 without much trouble, and maybe a bit more. If you are just interested in turning out parts and they are Taig-sized then you can't make too big a mistake going that route.

[Jason3]

Hi Chns,

This ebay seller: http://stores.ebay.com/CMTechTools has thread mills, and they tell you how to program a thread milling cycle - might be worth your taking a look.

I agree with Sansbury - if you can fit the parts you'd like to make on an X2, then that is likely the way to go. Kit or DIY would depend whether you're interested in making parts with the machine or working on the machine If the clearance under the chuck is an issue, you could use MT3 collets (I'm assuming the X2 is MT3 and has a drawbar?) They're readily available here - if we can get them I'm sure they'll be available anywhere! This would also get the cutter load closer to the spindle bearings which will help with rigidity and finish as well.

Let us know which way you decide to go.

Regards,

Jason

[g29cc]

I have one of the Sherline cnc mills. I bought a Demo model from a dealer that never cut anything but air. I walked out the door, with tooling, vise, 4 th axis rotary, and misc stuff for around $1900 or so.

It has done quite a bit of work and was a great learning tool for me. But it quickly ( within 5 months ) was not up to my standards. I need something big. Something strong and durable.

For me I should have researched a little more and really talked to people on here first ( if I would have known this existed at the time ). But I talked to Sherline and other people about Sherline that were "dealers" or happy with them. I was told they could do small production and things like that. What I found out is maybe small production out of plastic and aluminum. But any kind of hard material its not really going to last and will beat up the machine quickly. Which as a down fall I bought Sherline Lathe cnc as well from IMServe. I ll NEVER EVER buy anything from them again. I specifically asked them about cutting stainless on the machine. SURE it will cut stainless and other hard materials. What a joke that was. I bought the IMServe setup because of its threading capabilities. Which are a joke as well. I emailed and called for support when others told me they are good. And never got a call back or an email. They are local to me and wont accept walk in business. That should have been my first clue to run away......anyways......


The sherline is good and accurate mill for doing small aluminum and plastic parts. I cut mostly 1018 crs and things of that nature and while it does it, its not really suitable for production runs ( small 50-100 parts ).

I am now looking at a Tormach setup. Which blows it out of the water price wise. $10,000 to get you setup as a plug and play ( with coolant table and all the decent nice stuff ). But your getting a shop machine that was designed from the ground up to be what its supposed to be. Which is a hobbyist small shop cnc machine. The X series mills which some people directed me to with modifications can make a small hobbyist happy. But I think if your looking at doing serious production you need to really consider what your going to do and how big a part your going to do. The X series might totally work good for you in your situation. But dollar wise if we could all spend the cash , we would be looking at Haas Tool room mills or things of that nature. But seeing the cash you listed, I would say do ALOT of research before you do what I did and thats waste $4500 on machines that dont work half the time like I hope they would.

Granted my sherlines have paid for themselves ( mill was paid off about a month ago and the lathe is still working towards paying itself off ) , so I cant complain in a sense. Other then I wish I would have had more cash up front to get something like the Tormach first and been happy for a few years. Instead of being 6 months and kicking my ass everytime I sit down to the Sherlines.

They are great for the hobbyist and stuff like that. But serious machining, forget it. They are accurate , but I have troubles with working with them and I am not making rocket ship parts. I guess in some aspects, when going from a 30 hp Haas to this is a BIG BIG change. And I have to accept that. But still there are things I think it should do that it doesnt.

Good luck and ask , ask ask before you buy or commit to something.

Todd

[chns]

Thanks a lot for the help guys! I've definitely ruled out the Sherline. At the moment I'm leaning towards getting an X3 from grizzly or HF and making it CNC, but I'm a bit confused as to how to get that accomplished. As much as I love DIY and tinkering with things, this mill is supposed to be a tool to help me DIY and tinker, not something I have to DIY and tinker with to get running (I have very little knowledge in this area other than very basic manual milling so I don't have confidence in myself either).

So that leaves me wondering, if I purchased an X3 or tried CNCing my X2, what do I really need to get/do to pull off the job? Is there a guide or instruction set somewhere that would explain EXACTLY how to do it, or is this something I kinda have to work out myself? I checked out the conversion set from CNC Fusion where they sold a set with ballscrews for $569, or "premium" ballscrews for $949 (is there much to gain from that upgrade?) but that would still leave me needing steppers/servos, a controller for them, a way to interface with a computer, and a way to use the computer to control everything. I have absolutely no idea how to do this or what to expect for pricing.

Ideally, if there's a way to purchase a ready to use X3 CNC, or a comparably priced/spec'd system I'd pay a bit more, but its looking like I'm not gunna get it that easy on a budget. Any ideas? Thanks again!

PS: Two more questions to bother you guys with. If I'm trying to start a CNC routine at a certain part of a workpiece, how do I go about that? I've seen some people using what looked like a 3 jaw self-centering vice setup that seemed awfully like a lathe chuck, but I haven't seen where I'd buy something similar. Also, any suggestions are far as coolant goes?

[Jason3]

It sounds like you're more interested in getting a machine running with as little head scratching as possible. Perhaps the CNC conversion kit from Syil? I think it comes with everything you need to convert your X2, including the steppers and drive, or you could buy a CNC X4 ready to go if your budget would stretch to that. I seem to recall reading good things about Syil, but others here will surely know whether they're any good.

To start a routine at a certain point - if you're using Mach3 - move to the point and set the DRO's to zero (assuming that the part program you're running has that point as zero...) Have a read through the Mach3 manual - it's fairly long and detailed but should give you a pretty solid understanding of how it works.

The thing that looks like a lathe chuck likely is a lathe chuck That will reduce your clearance under the spindle significantly though - you might get the part lower by using a 'V' block in a vise to hold round stock.

[g29cc]

I would stay away from diy setup then. If you want to get up and start making chips, then just buy a plug n play setup. No matter what setup you buy for a diy your most likely going to be having to modify or sit there and say wtf ?

I was going to retro a Rong Fu mill. Its barely used, works great and best of all I picked it up for $400 10 miles from my house. After some thought, I figured it would be a great mill ( at 650 + lbs of rigidity ) , but with all the time to retro it and get it to work good, that I would be better off spending the money on something that is made to be a CNC machine , not a wanna be. So I ll be buying a Tormach when I have the $10,000 set aside.

Depending on the accuracy you want, the ball screws will play a BIG part in that. You can fiddle and play with lead screws all you want and get them good and tight. But you ll spend time doing that. For me , I dont have that kind of time. I am too busy making chips and selling parts. I need low maintenance and high reliability.

Choose carefully what you want, and triple check everything you hear. Talk to as many people as you can , and your in the best spot to do that.

Good Luck
Todd

[chns]

Okay, so here's what I'm thinking at the moment:

X3 from HF or grizzly - a little over $1k

From CNC Fusion:
1 x "Small-Mill CNC kit #4 - X-Y-Z with BALLSCREWS" - $569
1 x "Double Ballnuts on all axis" - $175 (I'll make the sacrifice of less travel to reduce backlash)
2 x "Heli-Cal zero backlash coupling" - $30
Maybe "Gas Spring Kit for the X3" - $79

From KelingInc:
1 x "NEMA 34 HIGH TORQUE STEPPER MOTOR 906 oz-in | KL34H295-43-8A (Single Shaft)" - $99
2 x "NEMA 23 BIPOLAR STEPPER MOTOR 425 oz-in | KL23H286-20-8B (Dual Shaft)" - 2x$49 = $98
(both more power than I need, but I called to try to find things that were in stock, and there isn't a problem with a little extra power... I think?)

From GeckoDrive:
G540 4-axis step motor controller - $299


If I'm not horribly mistaken (which I probably am!), that setup, a power supply for the G540, and a bit of work and I should be able to just hook it up to a computer and run EMC2. Do you guys see any problems or trouble spots to watch out for in this plan?

Thanks for all the awesome help and info I've been finding around this forum, BTW!

[sansbury]

Originally Posted by chns 1 x "Small-Mill CNC kit #4 - X-Y-Z with BALLSCREWS" - $569 1 x "Double Ballnuts on all axis" - $175 (I'll make the sacrifice of less travel to reduce backlash)

What is the difference with the "premium ballscrews" kit? Just wondering if you should be looking at that? Also wondering whether the Z-axis backlash will largely take care of itself due to the weight of the head.

(both more power than I need, but I called to try to find things that were in stock, and there isn't a problem with a little extra power... I think?)

Larger-torque motors are slower than small ones given the same voltage and current. My 125oz motors will spin 1200rpm with 24V, while I'm maxing out around 200 with my 425s. Though with 5-pitch screws, you don't need that many RPMs to hit an acceptable speed.

[cadmonkey]

IF I were to have gone with the CNCFusion kit I would have gone with the premium, at the time (I don't know if it's still the case) they were using Nook SRT screws which according to mfr literature don't deviate from the nominal lead by more than +/- .004" per ft - that wasn't good enough for me - I went to the XPR screws which get you to +/- .001". Ground screws advertise at +/- .0005" (and the exponential cost difference shows that...)

EDIT - I see that CNCFusion is now using Thompson ballscrews but the PDF link they supply doesn't specify which quality level screw they use - the standard Thompson (see page 5 of the PDF) is .004 with the others being special orders. - END EDIT

Weight of the head may take up backlash if you run the gibs loose, but then cutting forces can produce chatter in that backlash range if it's loose enough for gravity to keep the head down. I run my Z gib tight and there is a lot of backlash in my single nut non-preloaded setup but software compensates for it nicely - I'm not looking to do a lot of 3D profiling (Bas reliefs, etc.) so a small amount of deviation here (though I haven't experienced it after carfefully setting up the backlash compensation initially) wasn't really critical to me. It holds consistent enough for me through a program. Make sure that the motor you listed for Z (and the others for that matter) is within the current capacity of the new Gecko - seems to me that I set the current limiting on my G203v for the Z axis right around 3.75A for a 600 oz/in motor. Just be diligent.

EMC2 is a good choice - many will push you to another product but with the new version of EMC (currently 2.2.5 but 2.2.6 is due out VERY soon) it is easy to setup and modify. A basic setup can be completed in 15-30 minutes if you have all your driver and computer information available. I recently put a tutorial up on the EMC2 wiki page for running the wizard through a basic stepper setup tutorial (which was based on my X3 setup) and plan to add some more advanced tutorials once I actually finish some of the electronics details of my setup.

[chns]

Originally Posted by sansbury Larger-torque motors are slower than small ones given the same voltage and current. My 125oz motors will spin 1200rpm with 24V, while I'm maxing out around 200 with my 425s. Though with 5-pitch screws, you don't need that many RPMs to hit an acceptable speed.

Ah okay, I didn't realize the higher torque motors couldn't maintain the same speed. Do you guys have and recommendation for how many oz-in to use for the X/Y and Z axis, and where to find such motors? (Unfortunately I'm also on a bit of a schedule here, so I'm hoping to find a place that will reassure me they are in stock)

Originally Posted by cadmonkey [COLOR="Black"Make sure that the motor you listed for Z (and the others for that matter) is within the current capacity of the new Gecko - seems to me that I set the current limiting on my G203v for the Z axis right around 3.75A for a 600 oz/in motor. Just be diligent.

I was worried about that one too. The gecko site lists the max output for any axis at 3.5A. The kelinginc site says the parallel bipolar draw for the motor is 6.1A, but diagrams a series bipolar setup to allow 3.05A draw. Is that correct and applicable for my situation, or do I have to use a higher capacity gecko?

Originally Posted by cadmonkey IF I were to have gone with the CNCFusion kit I would have gone with the premium, at the time (I don't know if it's still the case) they were using Nook SRT screws which according to mfr literature don't deviate from the nominal lead by more than +/- .004" per ft - that wasn't good enough for me - I went to the XPR screws which get you to +/- .001". Ground screws advertise at +/- .0005" (and the exponential cost difference shows that...)

I wish I could select the premium set, but that adds a pretty significant chunk of cash on top and starts stretching my budget. Do you really think I'll see enough of an improvement to justify the $380 price jump? I don't mind paying that much more if I'm gunna see my money's worth in improvement, but I'm a bit worried it'd be $380 that disappears into thin air. Am I being too foolish about quality here?