[sco_27]

Hi!

Few observations from my own BT30 ATC spindle making:

-use ID 50mm/40mm bearings or both ID50mm. Ideally 2x SNR 7010.HV.U.J74 and 1x N1008-K-M1-SP, however it depends on RPM and type of lubrication. Mine is up to 8k RPM, now I know that you want to make BT30 about 15k RPM because of cutting speeds for small diameter mills you will be using.

-clamping force minimum 5000N! Anything less is only worth Chinese low-end spindles.

-do not worry about balancing the gripper and other "small" parts. It is only crucial to balance the shaft (of course the higher the speed, the better it has to be balanced) because it is the only heavy part. Mine is ~2,4kg, after balancing there is about 0,1g unbalanced on one side and 0,09g on the other side. The thing is that also belleville springs sit slightly different after each and every tool change, and you can´t balance that.

-make your own cylinder. Use products sold for making hydraulics pistons - they are selling chromed rods with tolerated diameter and also tubes with honed ID. Make "semi-stages" from water-cut alu blocks, O or X-rings as seal and dry bearings with some polymer coatings. Made mine for about 30€...

-do not forget labyrinth seals on both ends and air blow-off of lower labyrinth, so that dirt and oil from machining does not enter the spindle.

-many will dispute about making mechanism that creates a differential force (so that the bearings do not have to take force from cylinder). In my opinion - use it! It is not that complicated and can be easily incorporated into your spindle design.

If you got any questions, ask.

Merry X-mas.

Regards
Luboš

[Azalin]

You guys are amazing. Thank you both Mactec and Luboš.

This is going to be a complete DIY project with the cylinder.

[Azalin]

Sent from my GT-I9300 using Tapatalk

[Azalin]

Not bad. I guess.

[RustedOut]

Nope, not bad at all. Thanks for sharing, glad to see the plan work out. How much travel do you have before the end pushes on the pull stud?

Bob

[Azalin]

Thanks Bob. Travel is 5mm.

[Azalin]

I was doing some math, I think 5000n is too much for me as I'll use this spindle on a router. Arount 3-4k force seem to be ideal however I'd like to ask something about the preload. How much preload should I apply to the washers? Less preload means less force and more length in the spindle. I want the spindle as small as possible and have 3-4kn force so what would you recommend? The washers are 10.2mm ID, 20mm OD and 1mm thick.

I made sleeve for the gripper to test the opening-closing. No problems so far.

[Azalin]

Stack bellvilles back to back "...)))..." and the force is multiplied for the same travel. Stack then front to back, "...()()()..." and the travel is multiplied for the same force. The design I picked up somewhere has about 78 bellville washers in groups of three . like this...

((()))((()))((()))((()))...

Mark

Mark how do you get 5000n with 78 washers? What washers do you have?

My calculations give me very different number. I need only 3000n and 5mm stroke. The washers are 10.2x20x1mm. Safe deflection between 50% and 75% is 0.13mm so using the washers in groups of 3 makes 38 groups. Thats 38x3=114 washers.

Please correct my calc

Here's the data for the washer. Page 10