[carl0s]

Hi. I need to make a very simple part, and I'm frustrated that I can't do it (I need to make a wedge shaped exhaust flange spacer, to help angle a downpipe slightly), so I have decided having a milling machine would be great, and even cooler would be if it was CNC-ized.

Here is what I am going to buy, does this look OK to start with? Any advice?

Weiss WMD25 milling machine, from Hugh at Amadeal UK as the AMA25LV, expected delivery in about a month.
Geckodrive G540 controller thingy. I'm right in thinking that this thing interfaces directly with the motors, so no other circuitry stuff is needed, right?

Then I just need to pick three motors (for now), some ballscrews although at first I intend to have a go with just using the leadscrews to see if it works at all, and a power supply?

Am I anywhere near doing things right?

cheers,
Carl

[M250cnc]

Hi Carl,

The first thing you have done right is ask.

Now the problem, you will get conflicting advice, there are a lot of Armchair Engineers on here who haven't got a clue.

They may have a fancy website have a lot of posts on here but are legends in their own minds. All the gear no idea is another description.

Anyway you don't say if you have any engineering experience or indeed any machines/equipment.

So i will assume you haven't.

So the gecko G540 i would say not so good for a mill due to its low amp/volt rating but great for a small router.

This means that you will have to use lower power motors, again OK for a router not so good for a mill. In the UK i use Motion Controlled Products motors and drivers & PS

There are limit and home switches that can and should be added

For CNC ballscrews are a must as they allow the machine to cut in the optimum direction which is called CLIMB MILLING and although you can have backlash elimination that can overcome backlash it will never be as good as no backlash and you can't move in the optimum direction.

To convert the mill you could need the use of a lathe and a mill, now if the mill is the only one you have then you may have to keep assembling/dissembling it as you go. Especially machining the ballscrews.

This can take considerable time "Think Months" and if your not experienced then there will be a lot of mistakes made along the way before getting it CNCed.

Then after you have got it CNCed then there is the software to learn, i would heartily recommend Mach3

Then to design 3D parts you may need CadCam software this can and does cost thousands. I use OneCNC CadCam this is very easy to use but is expensive others are cheaper full of bugs and hard to use.

So this may seem very negative but i am being realistic it can be extremely frustrating at times but it can also be very rewarding. You could get a ready built CNC mill but my own experience of the RF31 is anything to go by it may still need work to get it to a high enough standard. One very important thing many miss, is a one shot lube system as this will stop the machine wearing out too soon.

If at the end of the day you just want a bracket made get someone else to do it. You will get it far cheaper and quicker.

Now i have CNCed a Mill "RF31" & a lathe "M250" but i have an extensive home shop more even than WidgetMaster who is a real engineer BTW

And i know how to use it

Phil

[carl0s]

Thanks for the advice Phil - it's very much appreciated. I am going to buy the mill and make the flange spacer 'by hand' (non-cnc), so then I'll feel like I've not wasted my time and money buying the machine, and, well, it'll just be sat there asking to be CNC converted :-) Except I'm going to buy the CNC conversion stuff right away.
I definitely need to do more reading. I only yesterday googled 'ball screws' and 'leadscrews' and found out what they are.. I have no idea at all, but I want to do it!
I need to find out what is involved in machining the ballscrews, and suitable bracketry for mounting the stepper motors. End/limit switches are something I did already know about, and that seems simple enough to me.

Do you think the choice of mill is OK?

I mainly use Ubuntu Linux on both my home laptop and office PC, so I'm hoping to have a go with EMC - linuxcnc.org, although if it proves no good there's always Wine, plus I have Windows on this netbook.
CAD/CAM software is something I can probably borrow from people, but using it is another thing. I tried SolidWorks the other day and got quite frustrated! I am aware that most people seem to use Mach3, so if it turns out that EMC is a bad idea, I will of course go the Mach3 route.

I'll take at look at MCP's website now. I think I have already been on there once or twice.

thanks again,
Carl

[carl0s]

I know I should read up on sizing motors and what not, but do you think this kit is suitable, if one was wanting to start collecting parts?:
http://www.motioncontrolproducts.co....&products_id=8

[ihavenofish]

2 things on this.

1: the g540 will be fine if you pick the right motors. theres some out there with 280 oz @ 3A in which will be more than adequate. alot of people put massive motors on tiny machines because they dont know any better - they think thats just what you need. you can do math on all this easily to find out what will and wont work. my version of this mill will get 180 oz in servos - delivering 180 oz in at speed which is the key (all the way up to a theoretical 800ipm for me). a decent 280 oz in stepper on a g540 at 48v 3A will push this machine up to 100+ipm with 5mm pitch screws and still have good acceleration. i use a g540 with 19v psu and anemic 180oz in (wishful thinking) motors and it runs at 100ipm on my kx1 with .1g acceleration. it cant be stopped with any amount of human force. it will rip vises off the table before stalling in a heavy cut. the Z runs at 40ipm due to dovetail issues.

2: grizzly in the usa is now selling these machines, so you can expect to see some people selling kits and parts for converting to cnc by summer. these might make it easier for converting if you are a novice or just want it done faster.

[carl0s]

Thanks nofish, that's interesting. Current thinking (as of a couple of hours ago) is that I may go with the MCP kit because cost is actually pretty similar, once I take into account 30% VAT & Duty on top of Geckodrive's $300 controller price. I do like the idea that the Geckodrive is a nicely integrated piece of kit though..

[carl0s]

Ball nuts are dear aren't they!

[ihavenofish]

Ball nuts are dear aren't they!

they can be. they dont have to be.

theres a fellow in toronto who has ball screws that i plan to use on this machine. they are taiwanese 5mm pitch c5 grade rolled screws. no backlash. i think even with shipping and tax he might work out cheaper than most over there. youd need to specify the end machining, which of course is dependant on what you use as bearings and couplings etc. he also sells a gecko kit with 3 steppers and cables for about $390cdn and a bunch of other useful things.

[email protected]
his name is george. (gio666 on this forum)

good luck. my machine wont arrive til april, so im just designing a bunch of ideas for now. hard to nail down specs with no measurements thoguh.

[carl0s]

I may get in touch with him, thanks. The screws aren't too badly priced, until they're machined that is. It's the nuts that I was remarking on.

[carl0s]

I am correct in thinking the screw comes just as a rod.. without nut, right? Only this one on eBay (just for reference,.. it's a one off 2nd hand item that I have no interest in buying) seems to have the nut with it, but not mentioned in the description:
http://cgi.ebay.co.uk/NSK-BALLSCREW-...item27af554e59

[M250cnc]

Carl

I use 4 Nm motors on my mill which is a similar size mill to the one you are suggesting.

I use the MDS 980 along with the PS705 PS That's 4 motors and 3 PS inc 4th axis although 3 motors and 2 x PS would be OK

Now there are people that will tell you that they can get 100IPM but not so good if you are cutting anything other than air.

I have my mill set for rapids at 2000mm per min and feed at up to 250mm pm

In my own experience when you have the tool snatch into the work by bad programming feed too fast etc this is where you will loose position.

This gets less with experience of CNC

Using low voltage PS like 19v will limit your top speed as speed comes volts and power comes from amps. Marris of Geckodrive recommends up to 25 times the rated voltage for the supply to the motor.

It is a site well worth the visit as he has lots of general information that is worth its weight in gold

You would be well advised to spend as much time as you can in manual mode as you are in control and can instantly stop if something seems to be about to go pearshaped.

As far as i am aware solid works is modelling software and cam can not be generated from it.

So Mach3 is windows and from what i have seen on their forum it will not run under Unbuntu, peeps have asked.

Mach3 does have some wizards but they are all 2.5D none are 3D

So if you have a solidworks file it may be able to be imported into lazycam, software included with Mach3 but it is very difficult to use from my own experience "Lazycam".

Your chosen mill seems OK one thing often overlooked is the height under the quill because that soon goes when you have a dividing head on the table and a chuck in the collet and i cannot see that info

Another thing with this type of mill is when you knock out the tool you can upset the tramming of the machine due to the tilting head. That is why i went for my machine, but it's a round column so you suffer with limited travel in the Z without having to re reference. I knew that when i bought it but it's not a problem as i also have a manual Bridgeport.

Phil

[ihavenofish]

I may get in touch with him, thanks. The screws aren't too badly priced, until they're machined that is. It's the nuts that I was remarking on.

usually you buy them together, as they have to be matched. a nut form one maker wont fit another makers screw - or even one from another series by thge same maker.

a complete set from george works out in the $300cdn range for all 3 axes after machining (with nuts of course). give or take a little depending on length and machining details.

one of the best prices ive seen for screws of this quality. ive seen them in person too (hes making me a router), they look good.

[M250cnc]

Carl,

I used the ballscrews and double ballnut from MCP and was disappointed in the extreme with the ballnut.

I had to modify it to get zero backlash which is actually now 0.025mm max which is good on this class of machine.

So if you order the wrong length it will be expensive making the housings for the ballnuts is also another thing that has to be considered, and this is where it is easier to machine the bore on the lathe and finish on the mill.

As i now know you are a newbie engineeeri cannot emphasize enough not to spend anything on the CNC till you have used the mill correctly.

There are lots of unfinished PROJECTS on ebay

Where in the UK are you ?

Phil

[carl0s]

Carl,

I used the ballscrews and double ballnut from MCP and was disappointed in the extreme with the ballnut.

I had to modify it to get zero backlash which is actually now 0.025mm max which is good on this class of machine.

So if you order the wrong length it will be expensive making the housings for the ballnuts is also another thing that has to be considered, and this is where it is easier to machine the bore on the lathe and finish on the mill.

As i now know you are a newbie engineeeri cannot emphasize enough not to spend anything on the CNC till you have used the mill correctly.

There are lots of unfinished PROJECTS on ebay

Where in the UK are you ?

Phil

Hi Phil. I'm in Sale, Cheshire/Manchester.

I don't have anything in Solidworks, I just decided to have a look at it, and thought I'd see if I could model the spacer that I needed to make, and I struggled!

Regarding not spending money on CNC until I've used the mill.. is this due to me potentially buying the wrong sized ball screws etc? If so then of course I understand that, and wouldn't buy anything like that up front, but how about motors & controller? At least I could watch the motors go whirr from my laptop and such like!

[M250cnc]

CarlOs

Mach3 is not classified to run on a laptop unless you use a Smooth Stepper, which is where my experience lies

It would be great if you could just buy a machine,convert it to cnc then watch it whirr, is not how it happens in the real world. although some people think that way.

If you bought a mill and couldn't operate it manually you would not be able to operate it by CNC

But you will have spent a whole load more money.

Something i haven't mentioned and you seem to be unaware as well is the cost of tooling for manual & cnc working.

It would be easy to spend another 1k on top of the cost for the mill.

Maybe if you would like to chat later PM your number, moby is OK

I'm going for me tea now.

Phil

[carl0s]

Quick question: a 5mm pitch ball screw, well, does the thread pitch translate literally to lateral movement? i.e. will a 5mm thread pitch equal 5mm of lateral movement per revolution? I notice the steppers do 1.8 degrees per step, or 1/200th of a revolution, so that means movement increments of 0.025mm per step, +/- 5% (FIVE PERCENT! That's huge! Isn't it?).

If the above is right, well, is that any good? A 40th of a millimeter sounds like a nice small increment to me, but 5% of any kind of large movement sounds like a scarily rough tolerance.

[ihavenofish]

Carl

I use 4 Nm motors on my mill which is a similar size mill to the one you are suggesting.

I use the MDS 980 along with the PS705 PS That's 4 motors and 3 PS inc 4th axis although 3 motors and 2 x PS would be OK

Now there are people that will tell you that they can get 100IPM but not so good if you are cutting anything other than air.

I have my mill set for rapids at 2000mm per min and feed at up to 250mm pm

In my own experience when you have the tool snatch into the work by bad programming feed too fast etc this is where you will loose position.

This gets less with experience of CNC

Using low voltage PS like 19v will limit your top speed as speed comes volts and power comes from amps. Marris of Geckodrive recommends up to 25 times the rated voltage for the supply to the motor.

heres some basic math.

if you crash a tool hard, your machine will likely stall. thats to be expected. if it didnt stall.. thats probably worse.. youll just break the machine. small ball screw supports tend to only be rated for 3-5kn. a high end 16mm ball nut is only rated for 7.6kn. the ones with slimmer shells like youll have to use on the X are more like 3-4000n dynamic loading.

the most tangential force this little machine can exert with its overestimated 600w motor is about 700n, which is of course never in a single axis direction. friction force on the Y with well adjusted and lubed ways is about 75kg x .5 x 9.81 = 370N with a loaded table. acceleration at .1G = 75n.

basically shy of 1200n.

a 5mm screw will churn out after losses 830n per 100 oz in of motor torque. so you need a mere 150 oz in for the worst case accelerating into the stupidly heavy cut.

the kind of cut you need for that is a half inch 4 flute tool in low gear at 1500rpm running full with, 1/4" deep, 9ipm in 4140 hrc30 hardened steel. thats a cut you wouldnt want to do on most low end vmc's let alone a 260lb desktop mill.

now your suggestion of 4nm. thats 4770N of linear force. that will likely destroy the support bearings and blow out a slim ball nut if you hit a hard stop not to mention completely surpassing the preload causing backlash.

theres a video on youtube of a g540 and some small nema23 motors pushing around a massive RF45 mill at good acceleration and speed. check it out. a little research will show you that motor sizing is critical, and bigger doesnt always mean better.

(a note to you m250cnc... when you make posts claiming that you know more than the "armchair engineers", its usually a good idea to actually know more, cause theres plenty of real engineers here too)

[carl0s]

I have noticed that tooling can be expensive. I am hoping to start out with some kind of el-cheapo essentials 'starter set', but we'll see!

[carl0s]

...

theres a video on youtube of a g540 and some small nema23 motors pushing around a massive RF45 mill at good acceleration and speed. check it out. a little research will show you that motor sizing is critical, and bigger doesnt always mean better.
...

I will check out the video. I was watching a few last night!
cheers,
Carl

[ihavenofish]

Quick question: a 5mm pitch ball screw, well, does the thread pitch translate literally to lateral movement? i.e. will a 5mm thread pitch equal 5mm of lateral movement per revolution? I notice the steppers do 1.8 degrees per step, or 1/200th of a revolution, so that means movement increments of 0.025mm per step, +/- 5% (FIVE PERCENT! That's huge! Isn't it?).

yes and yes*

* on the stepper, most modern drives like the gecko use micro stepping, so you get 2000 micro steps per revolution. these steps arent precise, but they are repeatable. they mostly serve to smooth curved and low speed motion paths. because they are repeatable, its possible to map the screw in mach3 resulting in absolute precision a bit better than .001", which is probably about all you can ask for these little dovetail machines, and good enough for most peoples work i imagine.