635 replies to this topic

[BrightStar]

As previously posted, Critical Speed = 265.5 divided By the Square Root of (jar inner diameter" - milling media diameter"). Optimum RPM is 65% of the Critical Speed

So for example, using the 4" 1.3 litre Inoxia jar with their 0.8" media, the Optimum RPM is 0.65 * 265.5 / SQRT(4 - 0.8) = 96 RPM.

For the lego mill shown in the video, estimating a 2.5" jar and 0.5" media, the optimum RPM would be 122 RPM - ie faster than you might expect... My first ball mill was made with borrowed Knex and was great for small batches.

Edited by BrightStar, 22 November 2006 - 04:00 AM.

[hoarp001]

Ok, so if the optimum speed is 96 and mine goes 53... does that mean i have to mill it for twice as long?

Thanks.

[Frozentech]

Ok, so if the optimum speed is 96 and mine goes 53... does that mean i have to mill it for twice as long?

Thanks.

I am going to take a guess and suggest you mill 4 times as long at 1/2 the optimum RPM.

[Mumbles]

I would say it is pretty linear. 1/2 the optimal speed, 2x as long. This is going off of the standard 4 hour mill time for an optimised mill. My mill should optimally run at 92 rpm. It however runs about 30 (darn rock tumblers). It takes around 10-12 hours to get a BP comparable to that from an optimised mill, or around 3x as long.

This is just a personal observation, and by no means is guaranteed to be consistant with other mills.

[Frozentech]

I would say it is pretty linear. 1/2 the optimal speed, 2x as long. This is going off of the standard 4 hour mill time for an optimised mill. My mill should optimally run at 92 rpm. It however runs about 30 (darn rock tumblers). It takes around 10-12 hours to get a BP comparable to that from an optimised mill, or around 3x as long.

This is just a personal observation, and by no means is guaranteed to be consistant with other mills.

Could well be. I wasn't sure it it was linear, though, and was going with the most pessimistic, that there was an inverse square relationship between speed / efficiency. In any case, there is a dramatic improvement with proper speed/mill charge.

[Wyvern]

Hi, i didnt see this site listed http://www.ukge.co.u...e.asp?PT_ID=382 which is whaere i have just bought a mill/tumbler from.

I'll let you know how i get on with it

Edited by Wyvern, 27 November 2006 - 07:56 AM.

[Spudgun]

I'm sorry if this is a stupid question but I can't get my head round this...
When working out the optimum speed, are all the measurements (jar and media diameter) done in inches or cm??

[pymp]

Inches, hence the " symbol.

[Spudgun]

oops hehe thanks!

[Night Owl]

Guys are these ok for a ball mill?? I'm a ball mill virgin http://cgi.ebay.co.u...1QQcmdZViewItem

Edited by shell shooter man, 29 November 2006 - 05:09 PM.

[Frozentech]

Guys are these ok for a ball mill?? I'm a ball mill virgin http://cgi.ebay.co.u...1QQcmdZViewItem

Well... sure ! if your milling jar is at least 50 cm diameter and your mill can handle at least a 30 Kg milling media charge weight.

Sarcasm aside, why not work out the size media you need for *your* application, there is no single answer, then go from there ?

[Night Owl]

Ok was looking at the quality, but anyway Wyvern how much postage did they charge and which mill did you buy? http://www.ukge.co.u...strPageHistory= they seem quite cheap.

Edited by shell shooter man, 30 November 2006 - 03:37 PM.

[alex000]

Ok was looking at the quality, but anyway Wyvern how much postage did they charge and which mill did you buy? http://www.ukge.co.u...strPageHistory= they seem quite cheap.

I was going to buy mine from there but postage was £6 i think so i got it off ebay, this was a while ago.

[Wyvern]

i Bought the 3lb single barrel tumbler, i cant remember how much the shipping was but if you want my advice go for the fast one as mine hasnt arrived yet

Edited by Wyvern, 03 December 2006 - 09:08 AM.