Belt drive in the works !

[Cruiser]

I have only seen one belt drive pic and it was external and would have eliminated the posibility of doing the air tool changer mod. So I have been looking at sprockets and belts and doing my home work and finally tore my gear box apart after ordering sprockets and belts from the local ! I am at the same time going to change out the spindle bearings i just put in with some new ones, I looked at the angular's and decided on precision ball with shields or one side seal with oil for the bottom bearing, I was also surprised to find in my tool box 4 super precision bearings that are same size as the top bearings, so i'll have plenty of those. My gear ratio will be 1.583 so soon i'll be worried about what i can do with the low speeds without gears to change, I have no idea what to expect there. After gutting my box and taking a good look and then taking a few other pieces out not needed and a couple that will be used I think i have a good solution to having my drive in the box with no oil or excess baggage. I found out that there is a trick to taking apart the bearing carrier assy for the spindle driver and I plan on using it to carry my driven sprocket. It looks like i'll cut the gear off but if i can keep it i'll maybe use it for speed senser if i can. Enough for now i spose, I'll be taking some pics as i go and have a few i'll try to wedge in here now.

[wildcat]

Very cool idea! How do you plan to tighten the belt? Best of luck.

[Cruiser]

I'm hoping i did my homework correctly and the belt just fits ! If i need to tighten it then i'll have to use an idler.

[ozzie34231]

I'll be interested in this thread, hope you take it to the end.
A few months before Aaron gave up the ship, he sold me a headless machine. I really didn't want all those gears and the movable spindle, etc., and he just happened to have a machine, less head.
I picked up a spindle with a Kwick switch end from a Huco machine on Ebay for little money; big sturdy spindle.
So now I'm mentally engineering the rest of the head.

If I might add my two cents to what you already have planned, I might suggest that a single belt cog ratio probably will not satisfy you even with a variable speed motor, unless you intend to use a very limited range of spindle speeds or you have a huge motor, (5 HP). A large surfacing cutter needs slow speed and good torque and if you're talking 2 HP and want to get up to 4000 rpm for aluminum you can't do both with a single belt ratio.
Hope this helps, not hinders.

Ozzie

[Cruiser]

Well Ozzie I have thought of it a lot and figure i'll just avoid the large cutters altogether. My concern would be with say a 1/2" em in steel. If i need more horse i'll go 3 or have to do a whole new engeneering scheme. 5 horse all come lower rpm's and i'd need a new ratio and not enough room for it without making a new box to put it all in and if that was the case i'd then pick on a 7 because i'd need new vfd as well no matter which way i turn so .... did ya hear me screem, i was defening. ! all i want is to get rid of the box noise and have a usable system again !

[BobWarfield]

This should be quite interesting. Bully for you, Cruiser!

I've been agitating a bit over the pulley ratio question myself. I think a vari-speed (variable pitch) pulley has been the best idea I've seen so far. You can pick them up off eBay sometimes pretty cheaply. Once I got one in my hand it doesn't look that hard to make one either.

Ozzie, be sure to post your adaptation of the new head, as that will also be quite interesting.


Best,

BW

[ozzie34231]

Hi Bob,
Please post a pic of your variable speed pulley and some idea of its size. I picked up 3 a few years back and haven't used them. I've looked for belts that might be suitable and can't really find something perfect.

I had a restaurant mixer that used two of them on a common shaft as idlers and that gave a very large range of speed. Looks to me like one of mine would give a range of ratios of 1 to about 3 or maybe a bit less.

I'm thinking I want my new head to have a range of 40 to 4000 RPM with good torque at the lower end. Electrically I can get 10 to 1 but not with much torque at the low end. So that probably means about three steps on timing pulleys. I think my DC motor turns 2550 top so I need 1 to 1 1/2 on the high end and assuming I don't want to go lower than 400 RPM electrically, I'd need 10 to 1 there.
That's too big so I should shoot for 80 or 100 RPM on the low end.
Ozzie

[ozzie34231]

I just spent a few minutes with my machinists calculator and even cutting 4130 steel with a big surfacing tool or a HSS mill, 200 RPM should be low enough. Don't remember where I got the idea that I wanted to go down to 40.

Ozzie

[Cruiser]

I have spent some time looking into the vary pitch & looked for the dynamic drive systems. I won't buy something like that off e-bay nor will i gamble with size's. Also with a dynamic drive you will need some way of sync'ing with mach for some applications, such as tapping. For the time being i'll put this into application when the parts come in next week, then do a discovery of what my torque will be in the low speeds. I must admit that a dynamic drive would be nice with an encoder > or < but I couldn't even find anything at all searching the net for sourcing info or units and i used all of my limited vocabulary. its like they don't exist.

[ozzie34231]

Cruiser,
After stripping the gears and stuff you don't need, can you estimate the weight of what you have left, (without the motor).
I'd like to know what general amount of mass is there.

Thanks,
Ozzie

[ozzie34231]

Another question Cruiser,
What belt size have you decided on, width, teeth per inch?

Ozzie

[BobWarfield]

Fellas, my notes on my own belt drive conversion and the vari-speed pulleys are on my web page here:

http://www.thewarfields.com/cnccookb...BeltDrive.html

I plan to use the vari-speed pulley to implement a simple Hi-Lo gear. In low gear, the spindle speed will range from 0 -2600 rpm, which will be fine for steel. Hi gear will be 2600 rpm - 8000 rpm, which should be great for aluminum and other soft materials. Within those ranges, Mach will vary the speed electronically. Since Mach already has provision to let a microswitch tell it what gear its in, it should be straightforward to keep it up to date on what's happening. I'm envisioning a 3:1 ratio on the vari-speed, which ought to be enough to keep the torque up reasonably well. We will see. I may fiddle with these ranges after thinking it over for a bit.

Frankly, I am most concerned at this stage about getting my bearings to live at 8K rpm. My project will be a long time in planning as I intend to get my mill CNC converted before attempting it.

For those interested in vari-speed pulleys, I would research the Go Kart torque converter angle carefully. That looks like the cheapest source. You'll want to ditch the centrifigul mode and go manual, but that should be an easy modification to one of those units.

Best,

BW