Rim Grinding-grinder Speed Effects

[Prawny Baby]

hey guys....

whilst playing with grinder speeds in my room reshaping a set of plaz pads to go onto my doublewide rim, it suddenly dawned on me that my grinding problems could be down to grinder speed....

i used to use a bog standard clarke £25 grinder, 600w motor, single speed, just ur normal trials riders grinder.... using 4.5'' metal grinding discs....

when i left that out in the rain it died.... so i invested in a really nice grinder.

still 4.5/5'' discs, but this time a 1200w motor and vairable between 6 speeds....

naturally, ive always been grinding on the highest speed.

its just hit me tonight that if im grinding with a disc speed FAR faster than most people, arnt my grinds in theory going to be MUCH smoother and finer?

looking at my grind now it appears to be VERY fine, with many small grooves all very close together.... when i feel it, it feels a lot like an old worn grind, its not sharp, or even rough at all :P

my rear brake doesnt work AT ALL right now.... it just slips constantly....

could grinding speed be my issue? i dont want to go and try 6 grinds on my rim to see which is best.... as its a new rim and id like to grind it as little as possible!

any ideas or suggestions would be great!

thanks guys!

desperate nick with no rear brake!

[Dr. Nick Riviera]

try doing the "strokes" faster?

in your endoooooooooooooooo

[ScotchDave]

I'd hink your right as the disc would smooththe girnd down much faster.

[Will Arnold]

i reccon slower would be better :P

shame mines fixed speed at over 10,000 rpm :P

[Prawny Baby]

i think mine runs from 2800rpm-12000 on speed 6. its proper quick though, you can tell by the sound it makes!

[Hobnobs]

Yeah, another vote for slower is better. I reckon you want to move the grinder as fast as you can over the surface, leaving big sharp bits far apart, more surface area? Whereas with lots of small bits it will have a smaller surface area to grip with.

[Swize]

If its a new rim does that mean you have an old one lieing arround or am i just trying to be clever and look for the ovious answer :P .

[Prawny Baby]

yes sam i do have an old rim lying around....

its a ronnie with 23 dents in it! and 4 cracks in the sidewalls....

want to buy it? :P

[jamesb]

See what works best on the old rim :P

[Caleb]

May just be a thought however, on milling machines etc the higher the revs the rougher the cut and lower the smoother so id think the faster you went the harsher it would grind.

maybe try just pressing on harder or going at a more direct angle?

[totaltrials]

Make sure the cutting disc has a massive curve on it, best using the thicker cutting discs to do that, so just get some old metal and grind away untill the disc is curved, you dont want it sharp.

Then do it in one fast motion across the rim, don't go over it, because if your going over it again and again you get uneven lines you want line after line after line with abit of gap not too close, if your really bothered try and smoothen your old grind off as much as possible then the new grind will be better.

Thats what I do anyway.

Phil.

[Prawny Baby]

curved disc :P :) :)

madness! ive always used brand new discs for grinds, as ive thought if i use an old disc ill get a rubbish smoothish grind....

hmmmmmmmmmm

very interesting idea phill!

i think im going to slow my grinder down to speed 4 (which seems more like it) and smooth it off before having a proper shot at it!

cheers for all the helps lads....

[Janson]

i have used the same disc to grind about 30 times now, it's well good.

you either have to slow the motor down or go even faster. slowing the motor down sounds more sensible...

[Swize]

yes sam i do have an old rim lying around....

its a ronnie with 23 dents in it! and 4 cracks in the sidewalls....

want to buy it? :)

See what works best on the old rim :P

:S

That ronnie though ; Bargin :)

[shovel]

i normally find its best grinding with a newish disc as the edges of the disc are still nice and square so it'll dig more sharply into the rim and give you a better grind

but yeah slowing the grinder down should make a big difference as if its too fast it'll be too fine and really smooth which is alright for the front, but not the rear

[Bigman]

Yeh, prawn i think it is that your grinder runs to fast, slow the bugger down and see what happens, u know what sort of grinds my grinder produces, BEASTS thats what..... Also tis your queer grinding style, In my opinion, like i have said to your before :)

Adam

PS: your bike looks FOOKIN GORGEOUS :P

[deagledaddy]

whats this 'passing over/across' the rim bollox.

I'm pretty sure you just move round the rim in a constant motion. No left to right movement of any consequence is needed!! in theory too fast spining disc and it will cut more efficiently, the slower it goes the more it will 'tear' at the rim, creating harsher/rougher surface. Don't move round the rim to fast though!

thats my thoughts on it anyway.

[petit_pablo]

Ive got a fixed speed grinder but i use the edge of the cutting disc and move it across the rim fairly quick.

[ScotchDave]

Sorry for the bump, but is it worth spending a wee bit extra to get the varible speed grinder or not?

[Barbara Logan-Price]

just go sick inot the rim proper jam the disk into the rim leaves a harsh mother of a grind!

[MasterOfGussets]

Sorry for the bump, but is it worth spending a wee bit extra to get the varible speed grinder or not?

Personally I wouldn't have thought so. But it depends if you want to experiment with how light or harsh they are I guess?

When I get around to buying a rim and have to grind it I'll be using a set speed grinder and controlling it through the speed you rotate the rim at and the pressure you apply to the rim.

I guess it depends how comfortable you are with grinding? I spend most winters installing Fireman's switches in brick walls and have gotten used to whipping the grinder out and making a dust cloud... if, however you're not too handy with a grinder you could try the variable speed option. I'd put this down to personal preference.