need help building a disc grinder

atakach

atakach

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Jan 17, 2008
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i have some drawings for a disc grinder i want to build with a double sided grinding attachment. the problem im having is im not sure how to wire the motor up with a forward/neutral/reverse switch. can any motor be wired this way or is it a special type of motor.

www.takachforge.com
 
Some motors are reversible, some are not - make sure yours is.
There will a diagram inside of the junction box on the motor that will
show wiring for CW and CCW rotation.

Figure out the difference. Assuming 2 wires need to swapped, you'd need
a 2 Pole, 3 wire - 3 pole etc, switch.

For CW-OFF-CCW switch you'd need a 2 throw On-Off-On _toggle_ switch. In other words, with the switch mounted in vertical position, you should be able to flip it up, down
and center.

Another thing about switches: some are "momentary" and others are "maintained".
You want "maintained" ones.

I also recommend to buy a rubber "boot" for the switch. It will protect it from grit and metal particles getting into the switch.

You''d want to have adequate amperage rating. 15A is good.

http://www.mcmaster.com/ , page 827, 846
 
You will want to wait on the switch until you get the motor unless you can tell ahead of time how many wires will need to be swaped to reverse direction. Usually it is 2-3. like rahidd11 said your switch will be a on-off-on toggle but you need to know how many poles, ie wire to switch. Also be aware that you will need a heavy duty switch. each Hp is 746 watts at 120 v is about 7 amps. Getting a switch rated at 10 amps per hp is not excessive.
 
I need to get a better disc sander too. I hope you don't mind me jumping in on the conversation. Maybe I'll have some helpful ideas... we will see.
I'm just going to say what I'm thinking. Please correct me if I am confused about any of this.

I have a HF disc sander and it is not good enough for flattening. My workpieces always come out slightly wavy when compared against a precision straight edge. I have given up on it. I spend hours and hours sanding on my surface plate instead.

I saw on Steve Johnson's DVD that he uses a foot switch with his disc sander.
It seems like the foot switch is critical when you are trying to flatten material. With a foot switch you can place your workpiece against the disc before turning the motor on and you can turn the motor back off before removing the workpiece. If you try to stick your workpiece against a moving disc sander, you will get chatter and you won't be able to get your workpiece nearly as flat. At least that's what I understand from the DVD and I believe I have observed this in practice.
I can't use a footswitch with my HF disc sander because it is too weak to start up with a workpiece applied to it.

I remember that Mr. Johnson said that the motor he used for his disc sander was made for a Swamp Cooler, it was a 1.5 HP I believe. Apparently those motors are pretty affordable when you buy them from a Swamp Cooler dealer. That's probably what I will buy, but I haven't checked into it yet.
 
I am not sure how flat is flat. I have a couple of ways to flatten knife handles and scales for folder and I dont need to start them with the piece in place. I made a disk sander from a motor and a plywood disk and it worked great. I needed the motor for something else and have regretted taking it apart. My guess is both the ends or at one end of the piece has been sanded more than the other, the fix to this it to use light pressure (very light), better sand paper, finer grit and turn the piece so different edges see the oncoming sanding grit. If you are using the HF sanding disks just throw them away. I will then sand on a granit block to make sure it is really flat, I mark the bottom with a pencil or pen and sand lightly. This will show high and low spots. I sand until all marking is gone, mark again and then sand. I really do not have to do much of this type of sanding on a typical scale or handle 2-3 min on each.

I believe if you try what I have suggested you will be able to get a good flat surface. The one advantage other grinders do have is speed, slower is better.
 
thanks for the advice. from all im really in need of a disc sander for grinding my blades. i have a kovel surface grinder i use for grinding all my damascus billets with that i use for stock removal and i use it to surface grind just the handle areas on my forged blades it gives a flawless and seamless fit. as far as the hf disc grinder the one im building is slightly more advanced. it has a grinding bar attached to the front of it and a bushing on each side that holds the knife vice in and you can set the bevel and grind one sid and then reverse the motor and grind the other and have identical bevels ground on both side with a little practice it is fool proof method of achieving identical grinds on both sides of the blades. but other than grinding blades its pretty much useless i will just continue to hand sand my scales it takes time but thats why there one of a kind pieces.


www.takachforge.com
 
Thanks for the input. I'll experiment with that some more. I did find my HF disc sander to be useful to start off with, before going to the surface plate.
I think you're right that I have been using too much pressure and I may have been using the wrong grits of sandpaper at the wrong time. Maybe my expectations are too high as well. I won't give up on that machine yet.

I'm making folding knives so flatness is pretty important. Once I finish flattening on the surface plate no light will shine thru when I hold my precision straight edge to the surface.
I'm using 3M SC sandpaper with repositionable spray adhesive from 3M.
I use a marker to see where I'm sanding. That's a good tip.
 
I bought a variable speed reversing controller off eBay, and hooked it to a treadmill motor. I've heard those motors don't last too long but my machine has been going strong for several years. I used a disc from Rob Frink at Beaumont Metal Works. Here's a link to how my machine looks completed, I didn't take any pics while I was building it... The disc grinder is a couple shots at the bottom of the page.

Grinders

Good luck with your projects! It's great fun making stuff, ain't it? :D
 
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