Belt Drive Conversion

[RustedOut]

Well, as promised last week, here's the start of a thread on a two speed belt drive conversion. I did manage to take a look at the existing spindle drive gear and it is a candidate for the pulley hub. The teeth need to be removed and then will yield a 3" dia. hub with what I believe is a 35mm bearing surface. The gear needs to be flipped over on the spindle, putting the internal splines on top. The existing bearing surface is long enough for duplex angular contact bearings placed face to face and a preload nut. I anticipate the seal being placed on the 3" dia hub right now, but there is some room to play with between the bottom of the hub and the top of the bearings. I intend to add a spacer there and that could become the seal surface real easy.

I've modeled a new top plate made of 2" thick aluminum with 1" removed from the bottom surface except for a boss for the bearings. Under that is a bearing plate to trap the bearings in the pocket. Really a simple machining job with a precision bore for the bearings and seal. Bearings are Nachi 35x72x17 angular contact priced just above $20.00 each. Not sourced a seal yet as I'm not sure of the specs on it. The only thing that goes in the old gearbox is the bearings, bearing plate and preload nut. Everything else is on top.

On top of the hub, I am heading towards bolting two timing pulleys to it with three or four cap screws. A 48 tooth on the bottom and a 72 tooth on top of that for now. I already had those models, but the tooth count can be changed. I'm liking a 1.6 ratio right now and a 44 tooth/70 tooth comes pretty close. There has been a little thought to that ratio, but I'm no expert on that so it could change. 1.8 actually takes me to over 6000 rpm without over speeding the motor. That takes a 40 tooth and a 72 tooth. I need to learn more about VFD's before I can commit to anything. Not sure how slow the motor can be spun without loosing torque. Should be easy to do 500 to 6000 rpm though, just want to get into the 200 rpm range if possible.

I haven't gotten to the motor plate yet, but it's an easy deal too. Need to measure the motor bolt spacing before it's finished and added to the model. The old motor to spindle spacing is right at 6", so that's what I'm working to. There may need to be a recess in the top plate for the motor shaft/pulley clearance. No biggy there.

The pulleys have some issues out of the box from the ones I've seen, so more shopping around is in order. The 35mm part of the old gear isn't long enough to mount the pulleys to directly, but an adapter could be made. Like I said, more research to do there. For my needs, I need the spindle sticking above the top pulley some for an auto drawbar.

So, enough typing, here's some pics to discuss. First the existing gear. Never did get it out of the bearings to measure the bearing surface. If need be, I'll by another one.


Then the 3D models. The pulleys are from another project, so they have some issues, but I'll fix it when I know what can be bought.


Bob

[fatboy55]

Will you be able to use the quill with your intended design?

[RustedOut]

There will be some limit use, but remember, the gear is turned upside down and on the top side of the top plate. The new top plate is 3/4" thinner than the IH version. Haven't done a study on the amount of travel yet, but I'm thinking there will be a couple inches less.

If a new hub were made, the travel could be retained, but this way is simpler.

Bob

[packrat]

No need to use the more expensive angular contact bearings for something like this. Radial bearings will work fine. The angular contact bearings are usually only called for when there is a need to resist end play in a shaft, like on the nose of the spindle. The top bearings a usually just radials. The pulley and belts just put side and radial loads on the bearings.

[RustedOut]

No more than the price difference, think I'll stick with the AC bearings. Sure, we're talking twice the price of a $10.00 bearing, but it won't break the bank for a pair of them. Already saved a bunch of time in choosing the original gear for the hub, so I'm happy there. It will be a good warm up for when I build my 4th axis.

Now if the needed vfd comes in at a nice low price, this shouldn't hurt the wallet too much.

Hope you all had a great 4th, I know I did.

Bob

[Cruiser]

I'm curious as to how you are going to mount the motor ?
Something you will need to take into account is some adjust ability of the belts, I found that the belts, although selected by cog count are measured on the OD of belt. This is what blew all my calculations out the window when I did my drive.
I also found that most motors of 200/440 option come from the warehouse as 440. This ended up being my main problem with lost torque, and I had no key or knowledge of how to look at it and determine how to determine it and assumed it was correct. My Bad !
When I was planning something similar to your idea, I planned to move motor off to side and more to rear, then invert motor and mount it on an articulating mount that was separate from the lid or top and firmly bolted to side of box. You will find that you will need an easy way of relieving and tensioning the belt quickly and easily. That is where a mount much like an auto's alternator would come in very handy. It would also allow larger circumference belts to be used. After what I saw with my idler system troubles, it makes better design function sense. Fortunately the cogged belts don't require tension per say, but only need slop taken up.
Good luck with your design, hope it all works out for you.

[RustedOut]

Motor will sit pretty much where the old IH motor is, just move it up on a swivel plate. And like you say, like an alternator adjustment. Actually a swiveling plate on a stationary plate. Stationary plate will bolt to my new top plate. An idler would be cool, but for now I'm just keeping it simple. I intend to pull the motor off the machine it's on in a day or two and get to measuring and finish the models of this conversion. Program the parts needing it and cut them.

My motor is a 4hp (3.53hp actual) european 3 phase running on 240v. I recall your issues with the voltage and that gives me hope I don't have to become a vfd expert to make this thing run like it needs to. You didn't have to did you? I don't recall your range of speeds and know you do a lot of aluminum, so a range of high speeds probably suits you. I do a lot of aluminum as well, but quite a bit of steel too. Sometimes alternating between the two. How low can you go on the vfd in the slower speeds and still maintain good torque?

The more I've thought about the 1.8 ration, the more I'm liking it. A 72 and 40 work out perfect to 1.8 ration using tooth count or pitch diameter. Thinking about flipping the pulleys in my model as the 70 tooth will fit the hub better than the smaller, and it won't matter on the motor shaft. These will be 15mm wide 5mm HTD belt pulleys, same as installed on the servos.

Problem moving ahead right now is money having just sent my car and house insurance payment this morning. And having not worked since last October makes having spending money difficult. But I'm about half done on some larger jobs in my shop that I think will pay for everything. Hopefully they are gone by the end of the month and I can move a head with this. This slow motion machining is hard to take.

Bob

[Cruiser]

I find that I can run my vfd down to 8hz min but try to min at 10hz which is roughly 500rpm, I don't recall the actual right now. I don't try to use a face mill but have no real problem with 1/4" EM in steel. Carbide/coated can be sped up quite a bit so I can get a practical cut with a 1/2" cutter, just can't hog it off.
mine is 2hp and serves nicely. I have a top speed close to 6,000 at 120hz at vfd and use it in alum.
I understand pee poor budget, I haven't had a decent job in too long, and busyness is not doing anything at all now for too long...................If I had some money I might be able to pay attention ! survival sucks !
Good luck at ya

[southernexplore]

You say you are getting about 6000RPM on the spindle at 120Hz how is that working as far as motor temp. and power with a 2HP motor and is your motor a 1750RPM or 3600RPM? I just received my Clone from Pat and after cutting some aluminum with 1/4 and 1/2 endmills I will be doing the belt drive mod as quick as I can.

Thanks,
Tommy

[Cruiser]

spinning up to 120hz is no problem with heat at all, in fact, I think I could go a bit more, but don't think I will. On the other side of the coin tho, going slow in the low hz range will make more motor heat even with the fan, which is the problem, so slow, no fan speed ! The motor is a 1750rpm ish and old school, heavy. The newer motors, supposedly have a better grade of insulation and can do the duty a little better. I always seem to learn some of my lessons a day or two late ! If it were wired correctly, I could have run my other motor even harder as it was an inverter duty motor, and had the better insulation on wires and core bonding, or something to that effect ? ! ? !
On the other hand this motor has a heavier shaft and bearing ! SO .........fair trade off ?

[RustedOut]

Like usual, I go into something thinking the opposite of what I should. After a little study on motors and vfd's last night and this morning, it looks like the motor I have is going to be a problem. Namely the faster rpm it has. Looks like it's better to start from a lower rpm and over drive the motor some than to do the opposite. Ok, lesson learned without any pain so far. Well other than now needing a motor as well.

Going back to the Marathon motors that I'd looked at before, I see there are several that fit my needs. There is an 1800 (1755 actual) rpm motor and a 1200 (1158 actual) rpm motor with the slower being higher full load torque. Both will safely over speed to 4200 rpm (3 hp versions). Departing from my thinking from the past couple days on this, it seems like the 1200 rpm motor would be the better choice. These are both rated at 1000:1 constant torque and are TENV motors.

But here's the rub, the faster one comes with a $663.00 price tag and the slower comes in at $944.00. That's a big bite out of the wallet. On the other hand there is one called a MicroMax in the 3 hp, 1800 (1760 actual) range priced at $523.00. It is a TEFC motor with a 1/20 of base speed constant torque. Max safe rpm is listed at 5400.

So, my math tells me the constant torque will be there down to 90 rpm with no gearing through the pulleys. That's a nice low end number. Now on the upper end of 5400, while not 6000, that's still a good rpm for all practical purposes although the hp drops off up there. Again with no gearing through the pulleys. I'll lose torque through any gearing to increase the rpm, so it seems that even though the rpm range is pretty good, the stacked pulleys is still the answer here. I can drop back to a 1.4 pulley ratio with the 1800 rpm motor, but I think the 1.8 is better for preserving and multiplying low end torque. And it'll keep from driving the motor to extremes, especially on the low end.

All that said, I guess the 182TC motor dimensions are what I'll model the motor plate to and figure on pulling the trigger on the MicroMax motor when the bucks find there way into my pocket. I'll change the pulleys to the 1.8 ratio, figure out the top seal and move on with the models.

Bob

[Cruiser]

Bob,
Inertial is what will run the cutter through the material in the upper rpm's, not hp. In the high rpm's you will be using an end mill or drill etc. that will easily keep going without loading out your inertia and stalling the drive. A large face mill might stall out the drive but it can't really take rpm's that high (5k/6k rpm's).
I felt the bite also when I was shopping the net for a new motor. I then remembered a motor shop across town who I trust and went to see him. He had racks of motors on the shelves which came out of all kinds of machinery's. He had 5 in house and access to many more on his network. I got a great motor and for a very affordable price. Sometimes it is really best to go local ! You get the face to face & some expert incite ! Also, while the motor was on his bench he looked at it to change the internal wiring from 440 to 220 for me and threw in some wire nuts. The price was less than $100 by a fair amount. I was looking for a 4pole motor, but carried home another 2pole motor, the primary difference between them for our use would be the final ratio of the drive we select. As I recall the 2 pole is 1800rpm & the 4 pole is 3600rpm. I don't know how it effects the overall torque specs between the two, which would govern the amount of inertia at the low end where torque would be used to keep a face mill going in a cut. In the top rpm's with end mill, it is all inertia. I do not know which would have the best low end grunt, I know that with my set-up, I have to take it easy or stall out. And by take it easy I mean that all I can do with my 2" face cutter is a light clean-up, no hogging what so ever. Hence, hogging with a good 1/2" hog end mill or toothed EM, and this is all figuring cutting steel. This is where your belt change ability will really pay off for you and having the low ratio run from 1800 rpm down or even 1200 down and do most of your cutting with the high ratio. you'll be happy with it if it all comes together.
OOPS ! I spent more than my 2c worth here again, now I'm broke ! HAHAHAHA ha ha