Fingers crossed it'll cut ally

**Jonathan** · 05-08-2010

Thanks!

I'm happy enough with the rotary table - it's very well made. If you get one I'd advise a vertex one as I've used this and a bigger one at school and they're both good. It's good in that it uses a worm gear (90:1) which means it wont move when milling but equally the worm gear is bad as it severely limits the rpm I can run the table at. I'm making the new axis because I want it to double up as a CNC lathe. My mini lathe (C3 from arc euro) isn't up to much so I'm hoping this will be sturdier.

I've machined the shaft of the axis the same as the mini-lathe so it can take the same chucks. Ideally I would have gone for bigger than 80mm diameter for the shaft...but turning that down to 35mm for the bearings took long enough and annoyed my teacher at school a bit... any bigger would have been pushing my luck I think!!

Any ideas for materials to use for the disk brake are welcome. The brake will only be used to hold in position, not for stopping, so heat build-up isn't an issue.

I'll go and take another photo...

P.S. Someone's bound to point this out, so before they do...If you look carefully on the renders of the 4th axis you'll see the disk brake is impossible to assemble! I've since fixed that by putting the disk the other side of the flange.

**blackburn mark** · 05-08-2010

Ah, im with you on the speed issue, i think i get you with the large motor to,, im guessing you would be fitting a rotory encoder for position feedback if you use the large DC motor ? (im no expert with these)

for the brake i would be looking at a motorcyle cluch plate maybe, im not sure youll get the force with electric solenoids to lock it for milling though but thats my guesstimation... id be tempted to consider an actual disk brake and caliper... the caliper would have to be beautfully fitted and have oposing pistons (you couldnt have it floating like you do on a vehicle)
im really not sure though im just thinking out loud :)

**Jonathan** · 05-08-2010

Originally Posted by blackburn mark

Ah, im with you on the speed issue, i think i get you with the large motor to,, im guessing you would be fitting a rotory encoder for position feedback if you use the large DC motor ? (im no expert with these)

Err I hadn't really thought about feedback. I was thinking something along the lines of using a stepper motor and the big brushless motor and switching between the two. For instance start by using the big motor for CNC lathe then switch to stepper motor to perform any milling on the part.
It would be good to switch back and forth between the big motor and the stepper but that of course requires the motors to engage at precisely the same point. Maybe get the brushless motor to stop at a set position (doable) and have another solenoid push a pin in the shaft to engage the stepper (tricky) ... the best would be to just use a servo but that's very very expensive to get anywhere near the power of this brushless motor.

Originally Posted by blackburn mark

for the brake i would be looking at a motorcyle cluch plate maybe, im not sure youll get the force with electric solenoids to lock it for milling though but thats my guesstimation... id be tempted to consider an actual disk brake and caliper... the caliper would have to be beautfully fitted and have oposing pistons

I'm not sure about the solenoids either, hence how I've milled spaces for several of them.
Clutch plate... that looks promising.

An actual brake disk and calliper would be very nice. Sounds expensive though. I don't know much about them - what would be required to actuate/use it? Are they available with small enough disks since the biggest disk I would want to use is realistically 6".

**blackburn mark** · 05-08-2010

i thought a servo motor was just that "a motor with a rotary encoder" maybe somone can jump in and help us on that one

you could make your own disk easy enough... the calipers would take to much effort compared to going to a bike breakers
you need to look over some motorcycles and posh mountian bikes for inspiration :) im sure some of the mountain bike disk brakes are machanical,,, could be worth a look.. the hydraulic ones would need a cam and lots of torque to actuate

**Ross77** · 05-08-2010

I'm just looking at spindle design and A/c bearings so I'm intrigued if you know of a cheap type.

im not totaly convinced a double row A/C bearing will be tight enough for ally, the ones iv got dont feel like they have that much pre-load, i might end up stacking the two of them

Do you mean rigid enough for milling Ali? If so be careful adding addition preload to a factory set tandem one as I believe you just end up un loading one side!!! if its a double row then lock it to the sharp end and fit a floating bearing at the other end.

According to SKF the distance between the CL of the bearings should be 3 to 3.5 time the shaft dia, so 12mm shaft = 36 to 42mm so a 100mm shaft should be way long enough.

The optimum design seems to be to use 2 opposing A/C bearings with a spring loaded pre-tensioner.

Have you seen the "DIY spindle design" on here, or these?
http://www.cnczone.com/forums/showth...t=12184&page=6
http://www.cncathome.com/spindles.html

It seems this has been done many times and the problems are mounting the motor to the spindle, the first link post no. 64 and 65 shows a flexible mount and water cooling for the motor.

I also have an ER11 collet and a RC motor to power it but as its for machine No. 2 I haven't got around to doing anything with it yet. so I will be watching with interest.

Good luck

**blackburn mark** · 05-08-2010

I'm just looking at spindle design and A/c bearings so I'm intrigued if you know of a cheap type.

"5200 zz z 2z ball bearing 10mm A/C" ebay aprox £16 for two... they might be to good to be true

just end up un loading one side!!!

och!! i hadnt thought of that... i hadnt decided if id just throw two in for good measure or pre-load them against each other
iv decided now!! cheers ross

According to SKF the distance between the CL of the bearings should be 3 to 3.5 time the shaft dia, so 12mm shaft = 36 to 42mm so a 100mm shaft should be way long enough.

i think you misunderstand, jonathan has a motor that has a 100mm long body so with a 100mm shaft there is no room left to add an A/C bearing and housing

yea iv seen those thread, they make interesing reading, one of those guys has his own ballancing machine!! to posh for me:)

**black5f** · 06-08-2010

Penis in pocket when around cnc machines is is a very good safety tip, no one wants to miss a tip :-)

**GeorgeD** · 12-08-2010

http://www.arceurotrade.co.uk/Catalo...raving-Cutters

**ecat** · 12-08-2010

I'm guessing we are talking about standard RC parts here so, the servo tester most likely outputs a signal of 20ms period. The width of the pulse within this 20ms period determines the output of the ESC. Actual values and their relation to each other depend on the hardware used.

Can the ESC be driven from a 0 to 10v signal? Not directly. I'm sure there'll be something on the web to suit or maybe this is another job for a friendly PIC.

**blackburn mark** · 12-08-2010

if you guys dream up a simple way of of conecting to mack3 ill have some of that :naughty:

im thinking of basterdising a lazor rev counter... can anyone tell me... will i get away with removing the lazor diode and pickup and extending them out onto my z axis and put the lcd somwhere more sociable?