designing a mill

[veteq]

Hello people,

after reading the forum almost every day i got hooked up.
First i was looking at a cnc ready benchtop mill.
the objective was to semi-design a high-end 1/10 rc car ( 0-90, under 3 sec. over 60mph top and racetrack handeling ) and than mill it at home.

now the problem is that the cnc virus got me

so now the objective is to make a small high-end (6mm end mill max. )
vmc

this has to be done before i have my degree in automotive engineering.

if this virus doesn`t come to a stop, the deadline will be the year 2047

just joking, ...................... 2009

remember a student isn`t the man with money, so this is a DESIGN thread, yes i`m working my ass of for the money. A nice machine will cost a couple off dollars. (euro`s)

the goal for this thread is to show the design off my machine, i hope you guys cann help me with some questions i have.

it would be great to let the expert with hands on experience shine there light without taking it to far.
i hope to give a few good questions with examples off some problems.
maybe it will help every one that needs it.


kind regards,

Roy Bakker
the Netherlands.

[veteq]

For education i have experience with solidworks, and his add-ins.
so i have solidworks 2005, with cosmos motion/works (simulation programs) also solidcam. the fun thing from school is you learn something.
esspecialy now because a compleet cadcam package and a little bit knowhow is fine when you want to use /design a cnc mill.

my design is made but will be redesigned several times i think, small/large adjustment?!?!

part for part i will show the design and ask wath i want to know.

for the base i think i want to use cast iron and let several surfaces be ground, this would be te best for the lineair rails and fixed/supported ballscrews.
i want to mound the ballscrew bearings (fixed in factory case) in a cast iron house with ground surfaces and matching holes for the bearing case
so the hide in vertical plane (off mounting surface ) is aligned.

my question is wath is the right type off cast iron for this design.
and is it posible to ground the green surfaces parallel and perpendicular to each other when the base is mounted like the assembly ( 2 parts ), or does it need to be done sepperate.
if thats the case the connecting surfaces off the base as to be ground parallel and perpendiculair. can this be done with enough accuraty?????

300mm width, 600mm high and the base is 100mm thick.

all questions, comments are welkom.

please tell if there is hands-on experience.

regards

[veteq]

The mill will be used for parts for a rc car, so this will be mostly aluminium and grafite/carbon plate (3mm).
mostly i will need to use drills and mills 2 till 6 mm.

10000rpm will be nice
2000mm/min feedrate
faster rapids maybe (not neccesery)
its almost only prototype building
need to work on 220V and max 15A

[veteq]

the parts i want to use are:

hiwin HG 20mm rails
hiwin 20mm preloaded balscrews
mcg ID-33004 brush servo ( 4 times ) 1.2 Nm const
gecko 320, grex, mach4
nsk astro psa 35 spindle 6mm max.
fixed supported bearings ( ballscrew )
gortite bellows
fogbuster cooler

the weight off the base is 190 kg. and moving parts, Z-axle is 30kg. xy is 55kg.

The basic calculations are made with the simulation program and are nice,
in all the cases of force on the machine the displacement is exceptable.
rapids with 4000N thrustforce no more than 0.01mm displacemend.

The holes for bolts etc. are made at the end en will decrease the stiffnes ofcourse, hope it will be exceptable ( do think So)

[chronon1]

Looks pretty good so far, you've done your homework and calculations .. 4000N thrustforce .. I have no idea how much thrust my 1/4"x20 and 3.5v 1.5A rated motors produce , ofcourse a powersupply pushing them is a 12V pc supply.

Course you have to convert 1/4 inch and 20 threads per inch to metric before being able to get Newtons of force. As always, please include friction into your calculation, which with an anti-backlash mechanism can be considerable !

Great CAD , is that solidworks ?

[NEATman]

Veteq-
Nice design so far! Solidworks is great isn't it. I have used it for the last 8 years.

One suggestion- If you invert the left-to-right travel axis, and mount the linear bearing blocks back-to-back, you will have a much larger work surface. It would make it more like a knee mill. This will help protect the ballscrew and ways of this axis, and also give you more table top work area.

Keep up the great work.

NEATman

[veteq]

Originally Posted by chronon1 Looks pretty good so far, you've done your homework and calculations .. 4000N thrustforce .. I have no idea how much thrust my 1/4"x20 and 3.5v 1.5A rated motors produce , ofcourse a powersupply pushing them is a 12V pc supply. Course you have to convert 1/4 inch and 20 threads per inch to metric before being able to get Newtons of force. As always, please include friction into your calculation, which with an anti-backlash mechanism can be considerable ! Great CAD , is that solidworks ?

yes it`s Solidworks.

torque =Force in N * ((lead in m / 2 * 3.14 ) * ( 1 / screw efficiency))

so
lead = 0.005 m is 5tpi
torque servo constant is 1.2 Nm peak is lets say 4 Nm
efficiency is 0.9 with ballscrew

1.2N = F * (( 0.005 / 2 * 3.14) * ( 1 / 0,9 ))
Fconst. = 1220 N
Fpeak = 4070 N

The nice part off lineair motion products ( rails, ballscrews ) is that there is almost no friction. The guys off hiwin told me after hours off talking that the total off friction force on this design is almost that little i cann forget about it.
The preload also cann be low because it is a light duty application for the parts.
Offcourse i have to think about heat generation and vibration.
but this is a bridge to far for me to calculate.
i made al the motion calculations by hand but its only a theoratical approah. i think its best to use a nice program for the pc on windows is best. then add-in a extra safety factor and try?!!?!?!

it can be downloaded by www.sureservo.com

regards

[veteq]

Originally Posted by NEATman Veteq- Nice design so far! Solidworks is great isn't it. I have used it for the last 8 years. One suggestion- If you invert the left-to-right travel axis, and mount the linear bearing blocks back-to-back, you will have a much larger work surface. It would make it more like a knee mill. This will help protect the ballscrew and ways of this axis, and also give you more table top work area. Keep up the great work. NEATman

It`s neat man that program SW
It would be great to work al day between SW and the designed part and then mill it on your own cnc mill
it`s so great i bought a pc and laptop special for SW with the special certificated grafic card. realview is nice. It`s like the best art for your brains.

Youre right on the x-axle.
i designed this type pure and only because it looks like a vmc and thus better. looks take over the sense off reality.
i hope i have the right solution on the protection of the ways and screw,
in the attachment in the blue circle i plan to glue a 2.5 * 2.5 alu strip.
then the chips have to become not reacheble to gravaty.

for milling my rc parts i dont need a large travel, this design is
x/y/z 280/170/170 mm
for 1/10 cars there is no part longer than 280mm and certanly not wither than 170mm ( car is max 200mm width )
nice movie here think no sound http://s97.photobucket.com/albums/l2...t=SV_A0005.flv

[daedalus]

Hi, are you planning on casting the base parts, or machining them from stock?

[veteq]

Originally Posted by daedalus Hi, are you planning on casting the base parts, or machining them from stock?

the plan was to machine from stock, would it be smart???
casting would be better because offf material properties i think, but it will be expensive.
i have a deal with a company with vmc, so this isnt that expensive.

[daedalus]

i think most people working with CI end up machining from stock, as casting is not exactly cheap, especially for one off parts.

I was just kinda hoping you had found a cheap casting foundry nearby, that i could then approach to do my parts (yes i know im in UK, but with the quotes ive been getting locally even shipping the whole thing from china would be more economical)

are you paying someone to surface grind the rail mounts on those parts, or do you have grinding facilities too?

personally im at uni still, so have a reasonable workshop, but they got rid of all their grinding machines, bar the smallest, so im likely going to have to outsource all my grinding needs. Dont even want to think what that will cost.

[sridharan]

Hi I think better you go for casting using grey cast iron,because this is the only material which has the property ,i.e to absorb the shock.Your design looks pretty good .
Hi i have one question to you actually me also desining a mini cnc mill almost the xyz meets your spec is it necessary to have such a heavy base.
Actually iam plotting my design using mastercam 9 software can you suggest me one software how to do simulation.Please help me on this .
Also iam looking for a counter weight for z axis if you have any idea please advice me.
Thanks.
Sridharan