Opinions needed on cnc bench top mills

I'm looking into getting a bench top cnc mill to start a small buisness making stuff out of acrylic and aluminum. Stuff like big acrylic dealer buttons for poker that I can sell on ebay. My main concern is accuracy and resolution I want to be able to cut parts with complex organic shapes and not have visible faceting so not much if any finishing work is needed. I found what looks to be exactly what I want on ebay but outside of the guys listing I can't find any info on it.

The auction can be seen here

http://cgi.ebay.com/ws/eBayISAPI.dll...MEWA%3AIT&rd=1

Other mills I have looked at have been mostly Taigs they are a bit smaller and don't offer a cnc and manual setup it seems to be one or the other. This mill on ebay does both and runs off of servos so it should be able to cut complex organic shapes better right? I noticed in his feedback he has one negative saying backlash is .018 and he used to post an accuracy claim of .0005 until that negative comment. I can't find any info on this machine outside of his auction and in an email he said he's been building them for 3yrs. If anyone can point me at other machines like this one to look at it would be great. Thanks -Mark

I am new to cnc but that machine looks like the one sold by Harbor Freight (made in China?). What kind of warranty/customer support does the seller offer? For that kind of money, I would shop for an American made machine.

If you doing any kind of intricate 3d milling and expect to be able to use the part without any kind of cleanup you need zero backlash, precision ground ballscrews and a solid machine. The one shown is nowhere near good enough to produce commercial quality parts. In addition, if you want to make any kind of money and not sit around for hours waiting for parts to machine, you will need a high speed spindle (at least 6000 to 10,000 rpm) and some decent feed rate capabilities (100 to 200ipm).

I would not even consider that mill. If you actually want ot make money off the machine it would be best to go with something more substantial. Others have already pointed out some of the needs for a machine to produce parts with little post machining work.

Frankly at the low end you only have two choices in my mind. One is to pick up a bargain real CNC mill at a resanable price (it can be done) or to go the doit yourself route with an import retro fit. Either way you are very likely to spend more than what this mill costs, but should get much better results.

Dave

Ok well I'm on a small budget $3000 is about max I can see spending for the machine alone. Software I already have auto cad and master cam copys from when I was in school. Can you guys give me some other machines to look at. I know going as big as you can is best but at this time this is as big as I will need. I'm only interested in making small things like dealer buttons as I said before. Making something like that out of acrylic I would want to run it on the machine to make the engraved picture then sandblast the engraved surface and be done. When I talk about what kind of resolution I'm looking for lets say I cut a 2" dia semi sphere out of aluminum. I would want a machine that can cut that shape without the need for any finish work other than buffing with a cotton wheel or fine grit sandblasting. Resolution is more important to me than accuracy if it can cut smooth but be off by a couple hundreths it won't really matter as I'm not making working parts but I suppose thoese two things come hand in hand. So how bout it show me some machines that I could use. If there is no machines that can do this within my budget show me ones that can that are over budget. Thanks -Mark

Resolution and accuracy are both important for your application. If the cutter positioning isn't accurate you will end up with overruns and gouges.

Given your limited budget, the only thing I can think of is retrofitting one of these

http://www.grizzly.com/products/item...emnumber=G0463

I think someone on the forum sells retrofit kits and you will have to piece together a controller, PC and Mach 3. I would use servos and high quality rolled ballscrews (hiwin) or better yet ground ballscrews (you find them sometimes on ebay). For your application you want to reduce backlash to the absolute minimum.

The only problem I can see is that the top spindle speed is really too slow for the small cutters you will be using. However, it would work and you could look at fitting a faster spindle in the future. Or perhaps you could look into a CNC router table instead.

pstockley has mentioned the Griz G0463 and pointed out some of its short comings. I'm not sure what size your dealer markers will be but you should make sure that the cross travel is enough. This is a light duty mill and is a bit under powered, especially considering the need to run high spindle RPM's. It may be feasable to pick up an air turbine spindle to chuck in the R8 holder for the smaller tools you are likely to use. The other option is to upgrade the spindle drive to hit higher rpms. The best option here is really an unknown until you get some experience with the engraving you will be doing.

Griz also has the G0519 which gives you more room to work with and about twice the mass. Cross travel is also improved so that is good. The bad is the much slower spindle which is bad all around for the materials you expect to machine. Further it might be a bit more difficult to up the speeds significantly. One good/bad thing is that the unit is three phase, so you do have some up side (limited) potential if you get a variable speed inverter. You will likely need an alternative spindle if you end up using extremely small tooling.

Look at Industrial Hobbies also. He has a nice (for the price) import that can be CNC'ed and if I remember correctly can be had with a CNC conversion. This will bring you closer to your limit as far as cost go but it is a larger mill with square columns good for CNC'ing. It also has more travel and about three times the mass. This is a much more serious machine and requires more consideration on where you put it. It does however give you many more options down the road. Industrial Hobbies does sell a nice CNC up grade kit for this machine which does cost a bit but it does appear to be high quality all around. Industrial Hobibies is often at Cabin Fever so if you go might be worth checking out. This is probablly more machine than yuo might first think you need so thought has to go into it.

If you do consider Industrial Hobbies then it would make sense to also look at some of Griz's knee mills in that price range. Good conversion kits will be expensive but a Bridgeport clone is a very flexible machine to have around.

No matter which way you go don't scrimp on the CNC end. For the type of work you are doing you need to be able to get very good repeatability and good resolution. For the X3 (Griz G0463) you could concieveably spend a bit more than the cost of the machine itself for a CNC conversion. Many though take the approach of buying through E-Bay and scrap deallers as this can have a significant impact on conversion expenses.

thanks
Dave

Thanks for the replys I didn't realize how big a machine needs to be to do quality cnc work. I still would like to give it a try though. I can see affording the X3 more but If I'm going to be close to $7000 of the cost of the industials hobbies machine I would probably just go with it if I can afford to do so. So what would I be looking at roughly to do a quality cnc retrofit on the X3 mill on top of the $1000 for the machine? Dealer buttons won't be any bigger than 2 1/2" dia 1/2 thick and I'll have to sell alot of them to pay for this though that is just a start to what I would eventually get into. CNC routers I hadn't even really looked at because I thought I was gonna get away under $3000 and haven't seen any close to that. I do really like CNC routers though we had a 24"x24" or so roland at school that could do the work I plan though I never could at school because their software couldn't handle faceting well at all cutting a circle with some 48 sides horrible. The only downfall to the routers is the minimal Z axis travel though I don't really know how much I will really need. Ok so if you guys can help me first by giving me an estimate on how much it will be to CNC the X3 everything needed to hook up to PC and second give me some cnc router suggestions and I'll go from there determining if I need something larger along the industrials hobbies end. Thanks alot you've all been a real help -Mark

Oh and also what to do about the spindle speed for the X3 how high can I get it up to and what kind of speed will I need with really small bits as your right that will be what I use alot. Thanks -Mark

Hello Mark;

As to the sixe of the machine for the parts you describe the X3 might make a very servicable machine. The machine doesn't have to be huge to do CNC. It does have to be stiff enough to hold the toleranve you want and the surface quality. I can't comment on the X3 with respect to these issues. I'd suggest visits to the web to look at CNC conversion varous people have done and look at the result of their work.

I really hate to even attempt to mention prices as there are so many options and quality levels that it would be difficult to hit the mark. As you can see Industrial Hobbies has a nice conversion kit with many American components and it costs more than the mill. You may or may not go over the cost of the X3. It depends on many things.

For one thing it is much a tradition in this field for people to scrap up some of the required parts for penneys on the dollar. It is possible to find leadscrew bargans on e-Bay and in retired industrial equipment. Even if you purchase leadscrews new from McMastercarr, Rockford or whomever there are many options that can leave your pricing all over the map. Going the machine it your self route on rolled ball screw assemblies will be relatively cheap, a ground zero bakclash high precision ball screw will cost more than the mill. The best thing I can imagine is that you find a vendor for an X3 conversion kit to provide a cost benchmark. You can then figure out if alternatives you find are a good bargain.

As to routers you can always go the do it yourself approach and build a machine from the ground up. Many have here on these forums. The big but here is that you need a well equiped shop to build a machine to do a reasonably good job in aluminum. One thin to consider is to build a router to do foam patterns and cast the buttons.

As to the X3, the spindle speed is probably a bit on the low side for what you describe, but I suspect you already have a background that is telling you that. It has been awhile since I looked at an X3 up close, so I can't say for sure what you can do to increase the spindle speed. I'd suggest that at the moment you just settle for the best that the machine can do and adjust feed rates. Down the road I'd get a air turnbine or brushless DC auxiliary spindle if this project proves to be viable. As to a router it is just like the mill conversion in that I can't say what it would cost you. Due to the machining of metal you will not be able to go the dirt cheap route like some of the wood routers seen here. On the other hand your buttons are small and doing something like a routeer coverign 12" square would likely cover you needs, especially if you have a lathe to cut round blanks to strat the process on.

Thanks
dave

Thanks Dave

Well I think I got my parents to give me some financial help to get one of the larger machines I'm 23 BTW. So I can either go the industrial hobbies route or get a decent cnc router like 24x24". The two have their ups and downs and I really can't say which would suit me best as I said before thoese buttons are only a start. A mill I can have both cnc and manual dial operation or at least thats what I think it looked like. A router has more work space but less z axis 6" being about the most I've seen which seems to be enough now. Most routers have very high spindle speeds but you have to use the computer to manualy control the machine. Which I guess would be easier than dials anyway I'm just not used to that, I would either do a run cutting an entire part CNC or use a manual mill doing certian cuts. So I guess it really comes down to deciding which machine suits my worksize needs more mill or router. I may end up wanting to do some stainless work down the road how does a router handle thoese harder materials. I'm gonna start a new thread on routers to give me an idea of what I can afford with them. Thanks again -Mark

could you use something like this.
http://www.taigtools.com/cmill.htm
if the parts your making aren't that big.it would fit your budget.

Mark,

I've got a Taig 2019CR and I would strongly recommend it for your needs. The max travel of 12 x 5-1/2 is well larger than what you need for your parts. You could easily build one up for CNC for less than $2000. Everything just bolts right up. I run rapid traverse on my machine at 108 ipm and have cut slots in aluminum with a 3/16" cutter at 18 ipm. You can get a lot done here for not much money.

This morning I was machining a part very similar to what you described. I milled a logo in a piece of aluminum 0.040" deep with an 1/8" cutter. Took maybe ten minutes at a pretty conservative feed rate. The finish was beautiful. I just ran steel wool across it a few times and I was done. You could probably run a Taig at 30 ipm cutting acrylic.

Send a post back or PM me if you have questions.

Scott

If you are interested in going the Taig route, I have one that is just gathering dust since I got my Tormach a couple months ago.

I bought mine from Denver CNC, so I have their Xylotex based 4-axis controller. It's been upgraded to the 1/4HP spindle motor and 280 oz/in stepper motors. I've never run mine much above 30 ipm, but I'm sure it would go a bit more. I'll throw in all of the Taig tooling I have, fly cutter, 5 of Nick Carter's tool holders, drill chuck. Also included is an old Trico Micro Drop Coolant system (less mess than flood or mist) that I picked up on Ebay for $160. It leaks a little, but it still works fine. Oh, and the 48x24 enclosure I built from 80/20 quick frame and 1/8" plexi goes too... I'm looking for around $1800 for everything...

If you're in Pittsburgh, I'm only a 3 1/2 hour drive away in Harpers Ferry, WV.

Let me know,

Dave

Thanks for the offer but I'm sold on the idea of a bigger machine now that I have financial support to afford it. I'm now in the market for either a CNC mill or router around $7000. Thanks -Mark

Don't forget to budget for tooling, both the expendable and the hard type. You seem to be forcused on specific usage at this time so your needs may be modest, but you are still likely to need some stuff.

Thanks
dave

Well there is a big difference between a mill and a router...the mill is generally sturdier and the router generally has a larger envelope.

I would look at picking up a used Bridgeport CNC and retrofitting it if the envelope is sufficient for you....