[raynorj]

Hi, I am conscious that many problems come when you try to run your new CNC with un matched component so I am looking for a source of Nema 34 steppers 600 oz or more that will run with Gecko G540 3 axis driver board rather than with three individual driver boards.
thanks
Rayna

[aarggh]

600oz/in is a fairly powerful level!

Are you sure you actually need that much or are you just worried about erring on the side of caution?

As a comparison, the 60cm x 90xm CNC machines from China commonly use a mix of NEMA 23's and 34's, at 260-around 380oz/in or so. And these are more than adequate for almost everything from wood and plastics to aluminium.

420oz/in or thereabouts seems to be the common sweet spot for the G540's given the 3.5A current limit, and to work within the parameters of the stepper itself for maximum speed and torque performance.

This vendor has a model you could run in series mode to be right on the G540 limit:

Nema 34 600 oz/in Stepper Motor

This guy in OZ has the same ones:

http://www.lowcostcncretrofits.com/steppermotors.html

But i'm sure you'll find plenty of others around. I just wanted to mainly raise the point in case you haven't actually sized the correct rating for your requirement, that in going up in size dramatically, it can actually be a trade-off in the torque/speed/performance/power used balancing act, and could actually have an adverse affect. Bigger is not always better.

cheers,
Ian

[raynorj]

Ian, Thank you for your reply which is most helpful. Short answer is no I have not done the calcs as probably beyond my skills. However have been watching for yonks as we say and considered that the the 380-425 oz range was possibly not gutsy enough for the new build in question. The machine has a moving table and is of very solid all metal construction with threaded rod x y and z drives. I need to mention that it is not my build but a friend and he as a model engineer certainly wants to mill steel components for small model steam engines and the like, side frames for G1 locomotives etc., so wood and plastic will not be often if ever on his agenda. Steel, brass and aluminium.
Maybe with that info it clarifies matters. I am more than happy to suggest to him the 425oz option along with the G540 if you reckon it is up to it.
many thanks
Rayna

[aarggh]

Hi Rayna,

Thanks, always happy to help. But as I always say, my comments are based on my opinions and experience, which as you may have noticed here on cnczone, everyone has a different opinion at times on the same topic. :-)

Having said that, I don't plan on machining steel but from what I've seen, it's a whole different class again, and you may well need a much heavier mass machine with more powerful steppers.

For this I would definately defer to the smarter folks here who have experience with steel machine on a CNC table, as mine is limited to alu and wood/plastics so i can only comment from that perspective.

From what I understand, the mechanical stresses, forces and torque involved for steel machining is much higher.

cheers,
Ian

[raynorj]

Ian, thanks again. Advice will be followed up on. While I have your attention!! though I would like to ask your advice machining what you know Plastics/acrylics plywood to 3mm thickness. I have built a Momus CNC mill for myself and in my case these are the materials I want to machine for model making purposes. 2D really, cut out type activities.
I have 380oz steppers and a Makita laminate trimmer router. Not quite ready to roll but wiring is now under way.
My main questions would be type of cutter spiral up down 2 flute etc. and feed/router speeds.
If you can help with that most appreciated.
regards
Rayna

[ger21]

It depends on the performance you're looking for, but, imo, a 600oz Nema34 is not a good match for a G540.

[judleroy]

The g540 may not be the right choice to run the motors needed for a large heavy duty metal cutting machine. Is it possible for you to post a picture of the machine? Good luck.
judleroy

[aarggh]

Ian, thanks again. Advice will be followed up on. While I have your attention!! though I would like to ask your advice machining what you know Plastics/acrylics plywood to 3mm thickness. I have built a Momus CNC mill for myself and in my case these are the materials I want to machine for model making purposes. 2D really, cut out type activities.
I have 380oz steppers and a Makita laminate trimmer router. Not quite ready to roll but wiring is now under way.
My main questions would be type of cutter spiral up down 2 flute etc. and feed/router speeds.
If you can help with that most appreciated.
regards
Rayna

Hi Rayna,

With 380oz steppers you should be able to power through light materials. Wood will be super easy, plastic is a litltle more difficult but with the right cutters still as easy as wood.

For my spindles I mainly use a mix of 1 and 2 flute cutters preferably upcut and in solid carbide, but also quite often in HSS and straight. The spirals give a nicer edge to the cut, and make less noise, this is important for plastic. The solid carbide cutters are a slightly lower rockwell hardness than tungsten tipped bits I think, so they aren't as brittle, and tend to really, really last! I use a 1/8" 2 flute spiral upcut bit for my acrylic stuff, and have been using the same bit for the last several months! I quite often the cheap 2 flute spiral HSS, and have used them on aluminium, wood and plastics without any isseus. i can also get feedrates up fairly high. The limiting factor for me is how many sharp angles does the toolpath take?

If it's doing circles or curves, whether it be plastic, wood or aluminium, I bump the feedrates up to around 2000-2400mm/min. With a spiral 2 flute spiral carbide it cuts smooth and doesn't make too much noise, and with a 2 flute HSS it's fairly similar. Using a 2 flute straight cutter however I drop the feedrate down to around 1500-2000 for wood and plastic as it chatters more, and around 900-1000 for aluminium.

If it's work such as the photos of the 4.5mm thick plexi-glass I've attached with curves but also a lot of tight angle work, I drop the feedrates down to around half of the above rates. These stands I did for a work mate I ran at around 1100mm/min, using the 1/8" 2 flute upcut spiral solid carbide cutter. I think I've made around 40 or so sets so far!

The problem for you though is using a router you'll be mostly limited to standard 1/4" bits commonly available, (read cheap!), which will mostly be 1 and 2 flute straight ones. I'm not sure how readily available spiral upcut carbide cutters are in 1/4"?

I'd recommend not bothering with HSS bits for your router, get the tungsten tipped ones, or even better, solid carbide ones if you can get them cheap enough will last you a long time. The solid carbide ones are extremely cost effective in the ranges available for the spindles. Far more so than I anticipated, and they last ages, and ages!

One hugely important aspect that will greatly affect the quality of the finish, the noise level, and the life and effectiveness of the cutter, is how well you can clamp the material down to stop vibration and lift. Especially so for rigid materials like acrylic and aluminium. If it can vibrate it will chatter, make an unholy racket, give a worse finish, and also possibly damage or at least certainly stress the cutter.

As you can see from the photos I have a toolpath that creates a bunch of 5mm holes around the perimeter of the sheet, and then I screw it down into the mdf base with screws every 125-150mm. You don't need much top-down force, doing plastics most of the force is lateral. MDF of course is a breeze to do and unless it's a really thin sheet, just needs a few screws to hold it in place, as it doesn't tend to move much unless the cutters are getting blunt. For MDF you'll need fairly fast feedrates as the dust will burn as you machine it otherwise. Which leads into the next issue, dust extraction. As you can see from the pics the waste build-up can be quite problematic, and can affect the machining, and heat up the bits dramatically, shortening the cutting life. To get a good finish, and extend the life of the cutters you really need good extraction.

There are formulas for calculating rates and speeds, etc, but to be honest, I generally go by the feel and the sound produced to determine if I can push it more, or need to back off.

Hope this helps a little more? I'm sure others will add their comments and experience to this.

cheers,
Ian

[ger21]

I'm not sure how readily available spiral upcut carbide cutters are in 1/4"?

Very readily available.
You can get 1/4" spiral router bits in just about any configuration, and for any material. MDF, hardwood, soft plastic, hard plastic, aluminum....

Router Bits, Cutting Tools & Drilling Tools | Onsrud.com | | LMT Onsrud
Vortex Tool: Solid Carbide Router Bits and Compression Spirals for woodworking, plastics and non-ferrous industries.

[aarggh]

Hi Gerry,

I know you can get them in almost anything in almost any config, but for me the cost is an issue, for example over here in OZ we get absolutely shafted on material, and especially tool costs. If a cutter in the States costs you guys $1, the same item costs us here $5-$25, depending on types, and spiral ones seem to suffer badly.

Power tools especially suffer from that, the Festool CT 36 dust extractor I've been looking at is around $500-$600 in the States, but is around $1100 here. that was the case when $1US was around $0.94AU. Great quality but just hard to justify, even more so with such a price disparity.

So I should have qualified "readily available" with "and cheap"! Over here many things are readily available, but aren't cheap, so all my comments are based with that personal perspective. :-(

I'm digressing slightly here and I apologise, but while we're on the topic of readily available, as an example, last week I went to the local (large) bearing supplier, looking for two new but different sized bearings, one of them a 7002 P4, for my smaller spindle, the guy quoted me $850 for a pair! After I realised he was serious and I stopped laughing, he said he could check as he could probably do me a discount. So for the two different sizes it would cost me $1700 to replace two slightly noisy bearings, I explained to the guy that I could buy an entire, albeit smaller, cnc machine with a spindle and vfd for the cost of the bearings from him!

The Chinese cutters I've been buying I must admit are really great quality and just last. They keep their edges beautifully. But even better, they generally only cost me around $2-$5 for each one. The exact same imported cutter from almost any OZ seller is around $15 each, more than half the cost of a ten pack from China!

cheers,
Ian

[raynorj]

Hey Guys,
thank you for all the extremely useful information. Ian I will get back on my plastics and cutters questions later but your answer so far is really helpful. I intend to make a collet set for the 6mm chuck on the Makita to suit any other cutter diams. Am also interested in following up your Chinese source.
Judleroy.. thank you also . I am getting a picture of the machine later today and will post. You will see that it is only SMALL but very robust and accurate. I would expect cutter to max out using maybe 3/8" endmills etc. and working in a small envelope maybe 12" x 4"x 2"H. but mostly 2D type applications.
thanks again all, Rayna

[raynorj]

hi again. thanks to all for input to now. Judeleroy you asked for a pic so here are three of my friends unit and one of my Momus design.
IAN where are you in Aussie? I get to Adelaide and Perth occasionally as I have kids there. i followed your blogg on the chinese CNC but have not found the one on chinese cutters..
Rayna