KMG questions - Noob Alert!

SHOKR

SHOKR

Well-Known Member
hey guys, today was the first day trying my KMG and i have few questions,

- my KMG tops at 2000rpm (according to an online calculator) however i *feel* its going slower than that, could it be voltage input thing or what? (note today before starting the inverter gave me an error of low voltage, but in a minute or two it worked fine)

- i need to push hard against the belt to see sparks and actually start grinding well (im guessing thats not normal) could it be because of the previous mentioned problem? can i compensate by using coarser belts? ( i tried 100 grit almost did nothing then used 40 grit so far)

- i bought the grinder used, and it came with ceramic plate for the platen, what exactly is that for and how do i attach it?

thanks guys
 
We need more info to trouble shoot the speed.

Is the drive axle turning 2000 RPM ?

What size is the drive wheel ?

For a comfortable top speed with a 4" drive wheel 3600 RPM at the drive axle is the norm I believe so 2000 would be quite slow and be the reason it's not grinding well for ya.

The low voltage warning was most likely just a blip in the power from the electric company- This is just an educated guess though.

100 grit belts are nearly finishing belts IMHO. They will remove steel but slowly and they'll wear fast. For rough grinding I'd go 60x 50x or 40x depending on your comfort level with grinding. Going slow is a good thing as a beginner !

A sharp 40x belt running full speed with firm pressure should EAT steel. Pressure grinds though so don't be afraid to use some while rough grinding.

A ceramic platen is mounted to the regular steel platen to reduce wear on the platen itself. With a typical mild steel platen the friction of the back side of the belt will wear into the platen making it no longer flat. This will be especially noticed when profiling blades and a groove will quickly get worn into the platen right over work rest height. The main purpose of the ceramic is to stop this from happening and maintain a platen thats truly flat which is important for a ripple free surface on your grinds.

Read this page for good info on the ceramic and install-

http://usaknifemaker.com/ceramic-glass-liner-for-flat-platen-2-x9-x-0-192.html

-Josh
 
I swear i wrote a reply this morning!!!!

Anyway, the motor tops at 1400rpm, the pulley on motor is 12.5cm, the one on grinder is 8.5, according to the calculator you told me about the output would be 2000rpm
The drive wheel is 4"

Well your guess is probably right on money, because this happens often here, specially in the summer with all ACs running like the fridge!

So to solve my problem i need bigger motor pulley? (or smaller drive pully, but with 8cm i cont think i can go much smaller)

Thanks Josh, always to the rescue! ;)
 
You may find due to available pullies you will be a bit under or over 3600 rpm at the driveshaft.

My take is that 3600 is a general guideline and if I had too choose I'd for over 3600 as opposed to under. You can always turn down the speed and the most likely scenario is that when you gain grinding experience you'll appreciate the higher top end for hogging off steel quickly.

Larger motor pulley sounds like your solution.

No problem, been there done that already :)

-Josh
 
mine (UK built KMG clone ) runs 4 step pulley the fastest is 12.5cm ( 5" ) to 5cm (2") which from my 2hp 1 phase 1450 Rpm motor gives me the 3600rpm, on a 100mm ( 4") drive wheel a good speed Which I use 36gt ceramics to eat steel and all grades up to 1300gt Norax finishing no slowing down all hardened steel

Im looking to upgrade to a 3ph direct drive with inverter and am running into problems as the 1450 motor can be driven to 100hz giving 2900rpm Ie the inverter can double the motor speed ( UK is 50hz std ) can your inverter over drive the motor.

Im having the Guy building mine look into getting me back up to the same belt speed as my old grinder as i cant use it very well slowed down the ceramic Belts wear out faster to

ATB

Duncan
 
hey Duncan
i think i know you from BB forum

my grinder came from UK with an inverter, its 50hz standard here too
i asked teh guy who conne ted it for me if it can go beyond the standard speed, he nodded but did nothing, now that i think about it, i dont really want to go beyond the standard speed even if its safe, im better off changing pulleys and be on the safe side!
 
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Josh, i did some calculations, and i blieve i'll have to change both pulleys, is there a minimum to the size of the kmg pulley? i feel its a stupid question but thought MAYBE would affect performance in any manner
 
Yes im on BB as well

Ping aly on there hes who builds the grinders i use
If you over run up to 100 hz and use a lower pully ratio you will get better torque
As pulleys step up speed they also step down torque
ATB
Duncan
 
Buy Ceramic Belts for rough grinding. I use Aliumnia Ceramic by Norton. Low cost for a excellent belt.
www.tru-grit.com call them. I don't think these belts are listed on their site yet?
Ask for the inexpensive Ceramic belts.

I use a 36 Grit a 60 then a 120 from this line for my rough and then a 220 Grit aluminum oxide, then it's off to heat treatment. Also even with the same Carbon percentage Carbon steel will spark much more than stainless steel when grinding.

Can't help with the rest of your questions I just though these tips & pointers would help you.

Laurence

www.rhinoknives.com/
 
thanks laurence

actually importing belts will be costly, and i still have to see available belts locally, will recieve 60 belts in different grits next monday.

will check if there are ceramic belts here but i doubt it.
 
maganinooo said:
emm can you explain that part further?
Click to expand...

Like a bike with gears if you change up you get faster speed wheel for the same speed pedal But it takes more effort so when you hit a hill its gets had work so you have to change down a gear to get more torque same happen on a grinder if you gear it up fast when you lean on it with a bit of metal you can slow it down easily

I use 36ceramic and then 200-1300gt Norax engineered abrasive i do ahve 120gt Ceramic but only use that on large wide bevels

on small bevels and Scandi grind i can go from 36 gt to 400gt the norax abrasives last a long time ie months so its worth importing a couple of each ive done a few hundred blades on my couple of sets and still going
the 36gt Ceramics do wear tho after a few blades
I do all grinding pre hardened

ATB

Duncan
 
i think i understand now, thanks Duncan

and i'll look into the belts, months does seem like a good investment :)
 
i did some calculations and i would want 15cm pulley on motor, and 5cm (or little bit bigger) on drive shaft, would that affect torque much?
the ones already in place are 12.5cm and 8.5cm
 
What FGYT is saying about torque makes sense from a scientific standpoint.

On my set-up though bogging just is not an issue at all.

My motor is a 3hp 1800 rpm and my pulley ratio pretty much doubles the rpm at the shaft (not exactly but within a few rpm's)

Perhaps you may have a different experience with a 2 horse motor but I think you'll be fine using the pullies to get the desired rpm at the shaft. I'm no electrician or scientist but using the VFD to crank up the hertz output just wasn't something I wanted to do. It may be perfectly fine to go that route and I have no sound reasoning for not wanting to do this just figured 60hrtz is whats supplied and what the vfd came set for from the factory so I stuck with it. That and pushing the motor beyond it's rated rpm doesn't seem like a good idea either (although probably not harmful to the motor since others run 3600 at the rated speed)

-Josh
 
thanks Josh, back from the weekend huh?! ( i do light stalking on FB) ;)

yeah thats how i feel exactly, so if i can do it with pulleys i would be much happier!
 
I got this aluminum cast pulley and will mill it and install on the grinder instead of the one i have, the one on the motor is 125 and the speed is 1400rpm (i have an inverter too)

According to www.csgnetwork.com/pulleybeltcalc.html i can leave it at 50mm and get 3500rpm, 45mm and get about 3888rpm or 40mm and get 4375rpm (i can get a measurment in between of course, but using these for simplicity.)

Now, would the 40mm be an overkill?
Thanks

20120726_135740.jpg
 
[video=youtube_share;4t-kkeFzKXU]http://youtu.be/4t-kkeFzKXU[/video]

Whats that sound?
I changed the pulley from 8.5cm to 4.5cm, so supposedly now the drive wheel tops at 3888rpm instead of 2000 (pulley on motor is 12.5cm)
However now i hear that sound its somewhere from the axle of the pulley and wheel just not sure where (i THINK the pulley side) strange thing is sound now appears even at speeds lower than the ones i ran before with the larger pulley.
Any idea why or what to do?
I tried oiling but didnt do much
 
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i tried it again at night and the noise was gone, is it possible oiling needing to 'set'?

will try grinding and see how it goes
 
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