[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

[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

[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]

...

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

[M250cnc]

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)

A note to ihavenofish if the cap fits wear it

Earlier you were claiming 100 ipm now you are saying 9imp with a crash

Now as i have experience of big cuts and i didn't mention crashes i mentioned a bad toolpath, this is a thing of the past as i am using better software now "OneCNC"

The power that is being quoted by this expert as coming from the motors will actually be coming from the mass of the table so when the table is moving at high speed this will cause serious damage "Think drop a heavy weight on the floor". I am talking about the table moving at a realistic speed of say 4ipm if the tool snatches into the work you will loose position you may break a reasonable size cutter at most.

The best way to see how much power you need is to put a spring balance on your machine with a one meter long bar as a lever this will tell you how much pulling power is needed. You will need to factor in actually CUTTING then allow some as headroom.

Statements like it will rip the vise of the table, yeah right.

As a rule of thumb a Bridgeport will have 12Nm motors a KX1 has motors rated at 1.35Nm according to what i just looked at, so if ihavenofish is to believed with that much power "0.303 492 074 23 pound-force" it will rip the vise of.

A much worse scenario would be to have too little power ihavenofish is correct in saying too much power is a bad thing as well.

So motors readily available in the UK will step from 12Nm 8Nm 4Nm and then there is a whole range of lower spec motors of around 2Nm and under.

For more reading here is a link to Wiki about Newton Meters http://wiki.answers.com/Q/What_is_a_Newton_meter

Here is a link for online conversions http://www.onlineconversion.com/force.htm


Phil

[ihavenofish]

i am far from an expert on cnc. i just use my experience with both my little mill, and our huge novakon nm200. add in a bit of basic physics, and i guess a youtube video doesnt hurt.

my kx1 motors are indeed 1.35nm on a good day with the right power supply. thats 180 oz-in. the motors im using on my BF20 will be 1.25nm - except they will be ac servos as opposed to steppers. i also have some 0.7nm servos which would also run the machine very well, but i found a kit that was easier to implement.

the servos on a DMG 635V are rated to produce 4500n force acording to their tech specs. thats roughly what you are advocating, except the dmg has 61 ft lbs of spindle torque, goes 1200ipm, has 2.5" ball screws, and weighs 8000lbs while pulling off half a g acceleration with 1300lbs on the table.

http://dmgcanada.com/query/internet/v3/pdl.nsf/8628a4d6da36fe00c1257368003b5226/$file/pm6us09_dmc6358351035v.pdf

if your gibs are so tight that friction is taking all your feed force, then you need to fix the ways and not just throw more motor at it.



anyway, bickering isnt helping anyone build a mill.

the pull scale is a neat idea, but maybe difficult to use in practice. an easier way is to simply put a torque wrench on the end of your ball screw when installed (not the stock lead screw). that will tell you exactly how much friction force there is. then just add in acceleration based on the mass of the moving parts, cutting forces of something you typically do which are easily calculated, and a bit extra.