BPinthemorning Posted December 27, 2008 Posted December 27, 2008 Alright, this is a long story, but I need help. With assistance from Swede, my dad helped me put together a real legit mill for a Christmas present (Awesome, I know). Well first glance this thing is awesome, but when I fire it up, its just not cutting it. Its a 1725 rpm motor, and here is how its hooked up: Pulley #1 (attached to the motor)- 1.75"Pulley #2 (drive shaft)- 4.75"Jar size- 6" When I run the motor it only getting 53 rmp. Thats not right. I don't know if the jar is slipping (its coated in 1 layer of rubber bands ;-) ) or if its just that I screwed up the calculations. Please check out my video ( ) and offer suggestions!
psymon Posted December 27, 2008 Posted December 27, 2008 What speed do you want to end up with? That seems like a pretty good speed for grinding chemicals if you ask me. My ball mill works at about 60 rpm. I have milled BP in it perfectly.
BPinthemorning Posted December 27, 2008 Author Posted December 27, 2008 Its a 1/2 hp continuous duty all enclosed fan cooled motor. It is running 110V and the roller is 1/2 inch plus the rubber tubing for traction. I'm hopping for a speed upwards of 80.
jacob Posted December 27, 2008 Posted December 27, 2008 What id is your drive roller *exactly*? I ask because when I put all your diameters in the Passfire calculator with a .5'' drive shaft I got 53 RPM for the jar speed, but when I put in .75'' for the drive shaft I got 79 jar RPM, might be a simple as changeing the tubing out. Have you tried running a loaded jar?
Swede Posted December 27, 2008 Posted December 27, 2008 Your motor has a 5/8" shaft, which is as standard as you can possibly get. I'm assuming (hoping) that you can adjust the belt tension a bit, because by picking up two or three drive (motor) pulleys of slightly different sizes, all you have to do is swap them out, and you can set whatever speed you want. Small changes at the motor pully can yield big changes at the jar. What you are probably seeing is a motor doing 1600 or so RPM rather than 1725, or a line voltage that is dropping a bit, or tiny slippage in the gearing... all of these can cause minor variations. And none of them are a big deal. You're going to want to vary speeds as your jar collection increases, and that's where a few spare sheaves (pullies) come in. If you can't find many small ones for the motor, pick up one or two more pullies for the drive shaft.
BPinthemorning Posted December 27, 2008 Author Posted December 27, 2008 I can't go to a 1 inch roller! the bearings are expensive, and I'm not buying 4 more... with a .55 inch roller diameter, what should I change my pulley on the drive roller to get 85 rpm?
swervedriver Posted December 27, 2008 Posted December 27, 2008 (edited) I can't go to a 1 inch roller! the bearings are expensive, and I'm not buying 4 more... with a .55 inch roller diameter, what should I change my pulley on the drive roller to get 85 rpm? What's the exact O.D. of the jar? 6" is the I.D., no? If your calculations were based on pipe ID, then your actual jar rpm will be lower than expected. Based on a jar (pvc? endcaps?) OD of say, 6.5", using a .5" bearing shaft with 4.75" sheave, and a motor shaft with 1.75" sheave, actual RPM of the jar will be around 49. That's if the motor is running at 1725 rpm. If you glue a hose over the 5" shaft with say, 3/32" wall thickness, this would increase your 6.5" jar's rpm to around 68. If you used a really thick hose, like a heater hose, garden hose, or hydraulic hose of say, 1/8" wall thickness, the rpm would be higher still, around 74 rpm at the jar. That would be a quick way, or you could get/make a new sheave. A 3" drive roller sheave would put the jar rpm at around 85, a 3.25" would put it around 79. YMMV, need to know the exact OD of the jar, if it's 6" pvc pipe, then the caps will be somewhere near 7" OD. Thanks for the exercise, I needed to do that calculation anyway. If you give exact circumferences of the jar, and drive roller, I can give you the exact diameter of the drive roller sheave you'll need to get 85 rpm at the jar. edit: btw, according to the passfire calculator, unless you're using golfball sized media, 85 rpm is to fast. Says you should be between 73 and 75 rpm with 3/4" or 1/2" ball media in a 6" ID jar. Edited December 28, 2008 by swervedriver
BPinthemorning Posted December 28, 2008 Author Posted December 28, 2008 Well I'm using .5" lead shot, so i need about 75 rpm then.The jar is 19.5 inches circumference, and the roller is 2.1 inches in circumference. I would rather buy a new pulley than a new roller sleeve.
BPinthemorning Posted December 28, 2008 Author Posted December 28, 2008 A tube to make a .5" roller 3" will have to be really thick... that would be hard to find.
BPinthemorning Posted December 28, 2008 Author Posted December 28, 2008 Frankly, I would prefer a different pulley so I could swap the belt on occasion if I move to a smaller jar, but I don't have passfire, and I obviously my calculations were wrong. Can some on help me with a different pulley size?
swervedriver Posted December 28, 2008 Posted December 28, 2008 (edited) Can some on help me with a different pulley size? The drive roller sheave (pulley?) you need for 75 rpm on your jar will be 4.33" diameter. A 4.5" will give you 72 rpm, and a 4.25" will give you 77 rpm. Passfire's calculator won't help with this math, though Sponenburgh's book likely would. I'm gonna buy that book I think. Hope that helped, I've got the figures done for my mill now too . Edited December 28, 2008 by swervedriver
jacob Posted December 28, 2008 Posted December 28, 2008 Frankly, I would prefer a different pulley so I could swap the belt on occasion if I move to a smaller jar, but I don't have passfire, and I obviously my calculations were wrong. Can some on help me with a different pulley size? Assumeing, Motor speed=1725 RPM Drive Pulley=1.75'' Drive roller=.66'' Jar od=6.2'' And you want the jar speed to be 75 RPM you want a (clicks calculate) 4.28'' driven pulley, a 4.5'' driven pulley will give you 71 RPM and a 4'' driven pulley will give you 80 RPM. That should be clear as mud.
swervedriver Posted December 28, 2008 Posted December 28, 2008 If the numbers you gave for the sheaves are taken from the outside diameter, then the calculations won't work I gave above, I'm hoping you measured the diameter/circumferences from the bottom of the belt groove? If not, our numbers won't give you the correct jar rpm you want. You say you're getting 53 rpm from a 4.75" sheave, a 4.5" sheave won't bring that up to near 80. Something's not right. xetap, thanks for that link, good stuff there.
Swede Posted December 28, 2008 Posted December 28, 2008 Think of it in terms of ratios rather than pulley diameters. First, assume the motor is turning 1650, not 1725. AC motor speed starts with a theoretical perfect speed based upon the frequency of the AC power. Then the engineers TRY to guesstimate losses, and come up with a number like "1725". The reality is it's probably a bit less. No big deal. Let's say it's 1650. Sheave diameters - it's NOT the OD, and it's NOT the bottom of the channel, it is a thing called "pitch diameter" as Xetap mentioned. But in effect you can ignore those complexities. The sheaves should have SOME diameter on it, either marked, or you know what it is when you order it, and this is usually the pitch diameter. So long as all the sheaves use a comparable way to measure, you're OK, because you are going to do ratio calculations. Let's say the sheaves are 1.75" at the motor, and 4.0" at the drive shaft. Very simply, your drive shaft speed is 1650 X 1.75/4.00. This gives you the RPM of the drive shaft. Knowing the diameter of the drive shaft and jar, again it's a ratio thing. The easiest answer is to have 2 motor sheaves, and three drive sheaves. This gives you six different speeds in a matter of minutes by swapping sheaves. I wouldn't get too hung up on exact RPM. Far more important is the media itself, and how the jar is charged. If the optimum RPM is 85, and you're doing 68, don't sweat it, the stuff will grind just fine, it might take 5% more time, or something trivial. On all my millings, I simply listen to the action of the mill. Your ear can tell you a lot about what's going on in there. Actual RPM is waay down the list as far as I'm concerned. Hopefully now you have a really sweet, sturdy, and large ball mill that can handle the big jars. Enjoy it and don't fret the RPM. If you want to get REALLY fancy, someday you can replace that motor with a 1/2 HP DC motor plus variable drive, or you can replace it with a 3 phase motor plus VFD. Both of these are expensive, but they would enable you to "dial-a-speed" at your leisure. Something for the future.
BPinthemorning Posted December 28, 2008 Author Posted December 28, 2008 (edited) Ya, thanks to your help, I was able to make a pretty awesome mill. I ordered another pulley for the shaft, its a 3.95" pulley, so now I will have 2 speeds. This thing is real sturdy, and now I just need to get some better media (I've been using nickels for the longest time) and maybe make a nice pvc jar (I'm using an hdpe protein shake jar atm). I'm probably going to get the .50 cal musket balls for media, but I will need a lot of them. Next project; 50lb bag of KNO3... Swede, check out my video youtube for a look Edited December 28, 2008 by BPinthemorning
Frozentech Posted December 29, 2008 Posted December 29, 2008 Ya, thanks to your help, I was able to make a pretty awesome mill. I ordered another pulley for the shaft, its a 3.95" pulley, so now I will have 2 speeds. This thing is real sturdy, and now I just need to get some better media (I've been using nickels for the longest time) and maybe make a nice pvc jar (I'm using an hdpe protein shake jar atm). I'm probably going to get the .50 cal musket balls for media, but I will need a lot of them. Next project; 50lb bag of KNO3... Swede, check out my video youtube for a look I looked at your video of it. Nice work on the construction. Another suggestion, get some heater hose from NAPA auto parts or other auto parts store, with an I.D. to slide *snugly* over your roller shafts. That will speed it up some, and give you a better gripping surface so the jars won't slip under load.
qwezxc12 Posted December 30, 2008 Posted December 30, 2008 I looked at your video of it. Nice work on the construction. Another suggestion, get some heater hose from NAPA auto parts or other auto parts store, with an I.D. to slide *snugly* over your roller shafts. That will speed it up some, and give you a better gripping surface so the jars won't slip under load. I'd second that. I know you solved your speed issue with another motor pulley, but when you load up that big jar with BP and a proper charge of media (read: HEAVY), that bare steel shaft won't grip the barrel at all. If it manages to rotate the jar at all, it'll be slipping, lowering your rpm and potentially wearing out your jar. Definitely add the heater hose to the driveshaft. I used 5/8"ID x 7/8OD (1/8"wall) heater hose on mine and it works perfectly.
BPinthemorning Posted December 30, 2008 Author Posted December 30, 2008 Well, qwezx I do have a rubber hose on the shafts, its just not the heater type... And ya, the gravity belt thing is a good idea, and it works really well, but my only complaint is a slight wobble in the table caused by the gyroscopic action of a hanging motor with a 1725 rpm... But all in all, this is a hell of a mill.
qwezxc12 Posted December 30, 2008 Posted December 30, 2008 (edited) Well, qwezx I do have a rubber hose on the shafts, its just not the heater type... And ya, the gravity belt thing is a good idea, and it works really well, but my only complaint is a slight wobble in the table caused by the gyroscopic action of a hanging motor with a 1725 rpm... But all in all, this is a hell of a mill.BPinthemorning, Gotcha... congrats on getting beast running! A good mill makes pyro sooo much easier... Questions- how do you like "gravity" tensioning of the belt? And what's the details on those jars? xetap, Like BPinthemorning, I think the gravity tensioned belt is the cat's ass. My mill can drive the big 12lb. jar filled with ~34lbs of media and 1200g of BP easily with no belt slip. The jars are Lortone 6lb and 12lb sizes. I got them here: http://www.therockshed.com/partslortone.html. Important!! - I put a strip of tape around the top seam to keep the lids from popping off when the jars get warm as the BP fluffs up...ask me how I know. I really like them; they have a octagonal interior to promote a cascading action, they're rubber, so they are a lot quieter than a PVC jar, and they have no neck or reducer, so cleaning them is easy. Video attached of the mill running with media only @ ~71rpm, from last year. Ball_Mill.wmv Edited December 30, 2008 by qwezxc12
BPinthemorning Posted December 30, 2008 Author Posted December 30, 2008 Qwezx, we have the exact same motor lol!
Aquarius Posted December 30, 2008 Posted December 30, 2008 Ok, lots of questions and here's another two: Heaterhose - what exactly is that? Is it some kind of insulating hose for radiator/AC and the like? Milling media - as for now I use 0.5 cal lead balls, but thinking about ceramics. Casting lead balls is a hell of a job.. I saw a post a while back on "sparkproblems" with these. What is the kind to get, any suggestions? Thanx
andyboy Posted December 30, 2008 Posted December 30, 2008 (edited) Ok, lots of questions and here's another two: Heaterhose - what exactly is that? Is it some kind of insulating hose for radiator/AC and the like? Milling media - as for now I use 0.5 cal lead balls, but thinking about ceramics. Casting lead balls is a hell of a job.. I saw a post a while back on "sparkproblems" with these. What is the kind to get, any suggestions? Thanx Heater hose is used in motors and stuff, goes from the motor to the cooler and vice versa among other things, found in biltema and other autostores. http://www.biltema.no/products/product.asp...p;iItemId=91017 Edited December 30, 2008 by andyboy
Mumbles Posted December 31, 2008 Posted December 31, 2008 I have no problems with using ceramic media. The main issue I see, is that unless you get them straight from the manufacturer, you never know what you're getting. I would trust nothing from an unknown source. Definitely not the cheap stuff from Texas Terra Ceramic Supply, and probably not even the stuff from Hobby Fireworks. I would possibly trust the stuff from Dave Sleeter, but thats about it. Anything else is a crap shoot. They'll work great for lone chemicals. I'd be leary to use them for anything live though.
Aquarius Posted December 31, 2008 Posted December 31, 2008 Thanks Mumbles, I remember seeing an article on Passfire regarding sparking ceramics. I'll might have to fire up the ol' furnace again, order some ceramic balls (!) and use the leadballs for milling BP and such. @Andyboy: Thanks for the tip, found it after a bit of thinking....
Swede Posted December 31, 2008 Posted December 31, 2008 Awesome ball mill! Well-crafted. It'll last a lifetime. The best part - I saw a bag of KCl in the background!
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