Disc Grinder Questions

[Colby L.]

I am pretty limited on space in my shop but would like to get a disc grinder for flattening scales and bevels. I am considering just getting a disc and swapping it for the drive wheel on my 2x72 when it comes time to use it. I am not a high volume producer so swapping wheels won't be a huge time hindrance to me. My grinder flips horizontal so I can use the disc in either orientation. Is there a reason besides the time to swap wheels back and forth that this would not be recommended?

A second question - is there a preferred vendor of discs? I have been looking at just grabbing a flat 9" disc from Trugrit.

Thanks all!

 

[N.W. Gean]

I have been using my disc in this fashion for a couple months now. It is extremely useful for flattening tangs and scales, however, you find it troublesome to keep switching back and forth. As soon as I can pickup another motor to hook into my VFD, I will do so.

I bought mine from USA knife maker, but I am not sure if it matters as everyone seems to ask about 100 for theirs. I am using one with the 1 degree taper, but I don't have enough experience to say if it is good or bad. You can find many threads where it is argued for one way or the other.

 

[weo]

I am using one with the 1 degree taper, but I don't have enough experience to say if it is good or bad. You can find many threads where it is argued for one way or the other.

Or we could do it here...I personally don't like the 1 degree bevel because it can leave a hollow in the grind. Having the bevel turns the flat disc into a part of a cone.

 

[N.W. Gean]

Or we could do it here...I personally don't like the 1 degree bevel because it can leave a hollow in the grind. Having the bevel turns the flat disc into a part of a cone.

We could, but I do not really have an opinion on the matter. I say use what you prefer.

It definitely muddies the waters if you have not used either, though. That is why I have no opinion on the beveled disc. If I used a flat disc now, it might make the tapered one seem terrible, but the beveled disc is the first I have used, so there would be a bias if I did prefer the taper.

 

[mknife]

I have both discs: The flat disc is excellent for leveling scales, guards etc. etc. The convex disc is a great help in flattening blades longer than the radius of the disc, the important thing is to apply pressure only 2-3 "from the edge of the disc.

 

[Crag the Brewer]

I'm interested in learning about Both too.....
I was leaning towards angled?

 

[Stacy E. Apelt - Bladesmith]

I use both, but the flat disc is most useful.
The argument that a 1° beveled disc creates a hollow grind is a little specious. Yes, technically it creates a hollow grind ... BUT, with a 1° arc on a 9" disc, the wheel size hollow it creates is equivalent to a 520" wheel (about 43 feet). The depth of the hollow on a 1.5" wide blade is .00009".

 

[Crag the Brewer]

I use both, but the flat disc is most useful.
The argument that a 1° beveled disc creates a hollow grind is a little specious. Yes, technically it creates a hollow grind ... BUT, with a 1° arc on a 9" disc, the wheel size hollow it creates is equivalent to a 520" wheel (about 43 feet). The depth of the hollow on a 1.5" wide blade is .00009".

Can you give some examples where the flat one is used?
if it's for small stuff (tangs, flatting scales) why not use an angled one? I'm trying to understand the need for both?

*I m making a disk grinder base that runs parallel to the floor, I just don't have the disk yet? I might make it, I might buy one?

 

[weo]

BUT, with a 1° arc on a 9" disc, the wheel size hollow it creates is equivalent to a 520" wheel (about 43 feet). The depth of the hollow on a 1.5" wide blade is .00009".

I should probably add to my response that I really only noticed it when I tried to flatten thin (<0.050) and wide kitchen knives using the 220grit disc between the belt grinder and hand sanding. The deepest scratches on the blade were deep enough that when hand sanding, I had to step back to 120grit to flatten the bevel again, whereas with the flat disc, I can go 220 on the belt grinder, 200->400 on the disc, then start hand sanding at 400 grit. This can be mitigated by changing the angle of the pull across the disc. To me, it's easier to maintain my pressure on the proper side of the flat disc than it is to change the direction of pull. It's also possible that I just need more practice...

 

[AVigil]

For long blades use the 1 degree disc. For all else you the flat disc.

 

[Crag the Brewer]

For long blades use the 1 degree disc. For all else you the flat disc.

I feel like I should understand this better..... But WHY use the flat disk at all?
with a flat disk..... aren't we Only using half the disk too? or does the direction not get thrown off much with the grind of the grain and possible movement (dangerous) of the blade?

IF you could only have one..? and you made Big blades often.
Flat or angled?

Thank You.

 

[AVigil]

I feel like I should understand this better..... But WHY use the flat disk at all?
with a flat disk..... aren't we Only using half the disk too? or does the direction not get thrown off much with the grind of the grain and possible movement (dangerous) of the blade?

IF you could only have one..? and you made Big blades often.
Flat or angled?

Thank You.

The 1 degree disc is a cone, so while that helps with a longer blade its only adding error into other things.

Flat discs gives flat results, 1 degree disc is not flat.

 

[Crag the Brewer]

The 1 degree disc is a cone, so while that helps with a longer blade its only adding error into other things.

Flat discs gives flat results, 1 degree disc is not flat.

The 1 degree disc is a cone, so while that helps with a longer blade its only adding error into other things.

Flat discs gives flat results, 1 degree disc is not flat.

I guess what I'm asking is on a flat 9" diameter (or whatever) size disk..... Are you using the whole thing? Or just on one half at a time.

Does your part cover the whole 9" diameter at once?

 

[AVigil]

I guess what I'm asking is on a flat 9" diameter (or whatever) size disk..... Are you using the whole thing? Or just on one half at a time.

Does your part cover the whole 9" diameter at once?

You can only use one side at a time ,

 

[Crag the Brewer]

You can only use one side at a time ,

Thank you.... But then... If you are only using one side at a time to flatten/grind parts, why not just get the angled faced version? So that you Could have the clearance so the larger piece isn't making contact with the abrasive surface? Why do they still make non-angled ones?

Thank you again.... I know these must seem like silly questions.

 

[AVigil]

Thank you.... But then... If you are only using one side at a time to flatten/grind parts, why not just get the angled faced version? So that you Could have the clearance so the larger piece isn't making contact with the abrasive surface? Why do they still make non-angled ones?

Thank you again.... I know these must seem like silly questions.

Because I do not want to have to factor in 1 degree when using the mitre gauge and table, also the grind is not at zero, perfectly flat, it is ever so slightly convex.

In making slipjoints 1 degree off is not acceptable and that 1 degree can multiply over the build.

You want perfectly flat? Use a flat disc.
You want a 1 degree off, use a beveled disc

 

[weo]

perhaps this will help explain what can happen with the cone (1 degree bevel) depending on how you pull the blade across:
The red arrow is trying to demonstrate what I was describing, and to avoid this (or have the beveled disc do the same thing as a flat disc) you would apply pressure at the blue x and pull the blue arrow. (Rotate the picture as necessary to get your comfortable angle. )

 

[Crag the Brewer]

Because I do not want to have to factor in 1 degree when using the mitre gauge and table, also the grind is not at zero, perfectly flat, it is ever so slightly convex.

In making slipjoints 1 degree off is not acceptable and that 1 degree can multiply over the build.

You want perfectly flat? Use a flat disc.
You want a 1 degree off, use a beveled disc

Oh it being convex makes sense why it won't make things flat....
That part wasn't known before, by me.
I kept thinking that.... Just stay on one side of the radius.
I wonder why they didn't do a true, flat bevel?

 

[AVigil]

Oh it being convex makes sense why it won't make things flat....
That part wasn't known before, by me.
I kept thinking that.... Just stay on one side of the radius.
I wonder why they didn't do a true, flat bevel?

Because you can not make a disc with a 1 degree angle and it not be a cone.

 

[Crag the Brewer]

AVigil
Oh.... I think I get it now...

I was thinking/worried about going over the center (red line) that looks flat.

You are talking about the green area creating a spooned out area?



Makes total sense, Now.
I was thinking 2D....haha, not 3D I guess

*Very informative thread!
Thanks.