Need some advice on a Diy rock crusher

[Grumpie]

I have a 3.5 HP Briggs and Stratton I would like to use for a small crusher. I'm gonna keep it basic with belts, hardend chain links for crushing and a hardend steel shaft running completely through the steel drum.
With a 3.5 hp how big of rocks should I feed it and how large should the drum be?

I leaning towards something in the neighborhood of 6" x 12" for the drum and a feed tube of 3".
For impact plates I was going to stack a few beads of hardend welds.

 

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[Grumpie]

I'm also debating weather or not to use belts and pulleys or an extended shaft with a coupler

 

[Mad Machinist]

For a motor that small stay with the belts. It won't have the power to blow through a jam and the motor won't like a sudden stop, think broken crank.

3 inch feed is WAY too big for a 3.5 horse motor. Stay under 1 1/2" max. And if you keep the feed under 1/2" your chains will last a lot longer.

6 x 12 sounds about right for a 3.5 horse motor. 4 x 12 would probably be better so your not pushing the motor.

 

[Grumpie]

For a motor that small stay with the belts. It won't have the power to blow through a jam and the motor won't like a sudden stop, think broken crank.

3 inch feed is WAY too big for a 3.5 horse motor. Stay under 1 1/2" max. And if you keep the feed under 1/2" your chains will last a lot longer.

6 x 12 sounds about right for a 3.5 horse motor. 4 x 12 would probably be better so your not pushing the motor.

Sounds good, just one more question, should the chain links be placed on the entire length of the shaft inside the drum, or should I leave a 1 1/2" area at one end for the rocks to enter without obstruction?
I want the feed to enter from the end of the drum but on top , but not directly on top of the spinning chains. If that makes sense.

 

[Grumpie]

OK, so if I go with a 1" feed do you think I could get away without the pulleys? I'm thinking with a 1" feed I could get away with a 3" wide drum and maybe 10" in diameter. Less chains inside the drum means less hardware and less fatigue on the components, at least in theory. To

 

[Mad Machinist]

Sounds good, just one more question, should the chain links be placed on the entire length of the shaft inside the drum, or should I leave a 1 1/2" area at one end for the rocks to enter without obstruction?
I want the feed to enter from the end of the drum but on top , but not directly on top of the spinning chains. If that makes sense.

The problem i see with that is creating a dead space for material to build up and the possibility of material being kicked back through the feed entrance.

 

[Grumpie]

The problem i see with that is creating a dead space for material to build up and the possibility of material being kicked back through the feed entrance.

OK, thx

 

[Mad Machinist]

OK, so if I go with a 1" feed do you think I could get away without the pulleys? I'm thinking with a 1" feed I could get away with a 3" wide drum and maybe 10" in diameter. Less chains inside the drum means less hardware and less fatigue on the components, at least in theory. To

With a direct drive, you would end up with your impact speed being to high leading to increased wear on the chains. Throttling the motor back won't work either as the horsepower and torque ratings are at wide open throttle. Throttle the motor back and the ratings decrease.

If I remember right, the ideal impact speed is between 1800-2000 rpm. I'll double check.

 

[jair]

12" drum max , rock 1.5 in max . No direct drive , the motor will not stand it for long and you need a sort of slippage , for the impact . I built a 4" x 16" with a 212cc engine , 6hp.
I can crush with mine 4" max rock but backed down to 3.5" rocks . I can put out 2200 LBS in a couple hours . 22 , 5 gallon buckets . Down to 200 mesh . Chains with hardened steel welded to the last link . Turns at 4000 rpms . Pulleys and one belt to allow some slippage , other wise you will kill the engine .

 

[Mad Machinist]

OK, so if I go with a 1" feed do you think I could get away without the pulleys? I'm thinking with a 1" feed I could get away with a 3" wide drum and maybe 10" in diameter. Less chains inside the drum means less hardware and less fatigue on the components, at least in theory. To

To kind of give you a comparison, the one I am working on is 12" wide and 20" in diameter. I'm using a 13 horsepower Honda and will be spinning actual hammers not chains. And I will still only be running at around 2000 rpm with belt driven pulleys.

Each impact will ever so slightly slow the motor down as it loads it. Gearing the rpm down increases torque to power through the load. The belts also serve to cushion the motor bearings from big impacts and vibration from unevenly worn chains or hammers. In a directly driven machine, those forces are transferred to the motor bearings. A big enough impact can overcome the oil viscosity, squeezing it out of the bearings, resulting in direct metal to metal contact between the bearings and crankshaft and ending in a spun bearing and motor seizure.

If the impacts speed gets too high, deformation of the chains or hammers happens much faster due to inertia of both the chains and feed material meeting. Deformation equals heat. Heat equals work hardening. Metal will only go through so many deformation cycles before it gets work hardened, becomes brittle, and breaks. I know it sounds weird but it has to do with inertia, modulus of elasticity, and a whole lot of other engineering concepts.

Sorry for getting all technical but in all seriousness, this is your machine. We can give you advice but in reality build it the way you want, break it, find out why it broke, and rebuild it better. That's part of the fun in this game.

 

[Goodyguy]

Great advice from the above posts.

In my opinion a motor that small is not hardly worth the effort of building a crusher.
Sell that motor and get at least a 6.5 hp or larger.

Yes you can build a mini ore crusher with your 3.5 hp but if you plan on crushing more than a few small chunks you will soon want a larger one.
Otherwise you will be spending extra time busting ore by hand to make it fit.


GG~

 

[Grumpie]

Great advise from the above posts.

In my opinion a motor that small is not hardly worth the effort of building a crusher.
Sell that motor and get at least a 6.5 hp or larger.

Yes you can build a mini ore crusher with your 3.5 hp but if you plan on crushing more than a few small chunks you will soon want a larger one.
Otherwise you will be spending extra time busting ore by hand to make it fit.


GG~

Yep I can understand that. When mad machinest said 1 1/2" feed should be max, I got that same impression. It's gonna be a portable compact unit for sampling.

 

[Goodyguy]

Yep I can understand that. When mad machinest said 1 1/2" feed should be max, I got that same impression. It's gonna be a portable compact unit for sampling.

In that case you don't want it so heavy that it takes two men and a boy to move it.

Mine weighs somewhere around 200 lbs. and it's small as crushers go.
Pretty much all I can handle by myself.




When portability and weight are an issue I use a ramrod and tube for sampling.....



GG~

 

[Grumpie]

Just out of curiosity, what would a 140cc Briggs and Stratton equal in HP? This engine looks slightly bigger to me than my 3.5 hp

 

[Goodyguy]

Just out of curiosity, what would a 140cc Briggs and Stratton equal in HP? This engine looks slightly bigger to me than my 3.5 hp

My 6.5 hp is 212cc so the math would put the 140cc somewhere around 4hp ?
However displacement is not really a true indicator of hp

GG~

 

[Mad Machinist]

Just out of curiosity, what would a 140cc Briggs and Stratton equal in HP? This engine looks slightly bigger to me than my 3.5 hp

4 to maybe 4.25 hp.

 

[Grumpie]

We'll, I ditched the 3.5 HP gas engine rock crusher idea and got this 6.5 HP at HF for only $108 otd. This "little engine that could" got great reviews so I thought what the heck, I've blew more $$ in Vegas in 5mins.

 

[Grumpie]

Here's a look at some specs

 

[Goodyguy]

We'll, I ditched the 3.5 HP gas engine rock crusher idea and got this 6.5 HP at HF for only $108 otd. This "little engine that could" got great reviews so I thought what the heck, I've blew more $$ in Vegas in 5mins. View attachment 1418826

Thats a good little engine, same one I used on my crusher. Just follow the owners manual for proper break in and it will serve you well... It may vibrate a bit at first during break in but that will soon smooth out with a little run time.

GG~

 

[SaltwaterServr]

Same brand I have on mine as well. Runs pretty dang good.