How much torque is required to operate a barley crusher?

Question

How much torque is required to operate a barley crusher?

Keith Hoffman

2012年12月26日 16:07

Question: How many in-lbs or ft-lbs of torque are required to crush barley using a mill such as the Barley Crusher?

Motivation: I'm interested in motorizing my Barley Crusher. There are endless blogs entries and such on how to do this but the parts used often vary based on industrial salvage or the cheap motor of the week. Selecting equipment for this type of project requires a minimum torque specification I don't have, hence the question.

No guessing please; I'm looking for a definitive answer for the community.

Topic mill homebrew

Category Mac

Keith Hoffman · Accepted Answer · 2012年12月26日 16:07

1

Keith Hoffman answered at 2012年12月26日 16:07

I've accepted mdma's answer but also want to throw out the number my local homebrewing community suggested: 50 in-lbs. This is very in-line with mdma's better documented answer. Happy automations!

mdma · Accepted Answer · 2012年12月11日 23:04

I've built 2 motorized grain mills. The first used a 600w (input power) 3/8" drill. It worked well enough with a loose crush (0.040") but I ended up frying the drill when trying to crush at 0.035", so this is a good candidate to gauge the minimum torque.

A 600W drill produces about 380W mechanical output. I was using this on just under half power - the drill used PWM to reduce the motor speed. The rotational speed, was 240rpm, or 4 rps. This gives a torque of

 T = 190 / 2 x 3.141 x 4
   = 190 / 25.128
   = 7.5 Nm

That's about 66 lb.in.

However, unless you can get a motor with a rpm that matches the sweet spot for milling grain, 120-260 rpm, then you'll have to use gears, sheaves, PWM, variac or some other speed controller to regulate the rotational speed of the mill. All of these have an affect on the torque - most motors spin too quickly and so you'll need to slow them down, which increases the torque if using mechanical speed control. This makes the torque of the motor less of a pressing issue. This leads to the typical advice found in the forums that a 1/2 hp motor is more than sufficient when used with speed reducing transmission.

My second mill used a 340W washing machine motor, with a 1:15 sheave. This offered more than enough torque - the limiting factor was the belt slipping, which happens on the rare occaision I get a rock in there, or when I inadvertently drop the feeler gauge in the grain chute!

brewchez · Accepted Answer · 2012年12月11日 22:06

If you don't want speculative answers based on what might be other users real experiences, I suggest contacting the Barley Crusher people directly.

So few homebrewers are being that specific about the torque in the way they use the mill that I think you'd have to cruise many forums to find the 1% of the brewing populace that has already done the homework and found the precise amount of torque required.

How much torque is required to operate a barley crusher?

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