horizontal vers flat disc grinder

Horizontal grinders would be great for edge finishing and other detail work. A disc grinder works great for finessing and finishing blade bevels and establishing true flats, and I've heard of a few makers who have made knives start-finish soley on a disc.

A flat dist of 9" diameter means that the longest length you can grind easily is 4.5" Anything longer than this, and you cross the center of the disc. That means that you have one side of the knife in which the paper/grit is going down while at the same time, on the opposite side, the paper/grit is going up. This creates a rotational moment in your work and makes it very hard to easily control the blade. However, flats are truly flat with a flat disc.

A beveled disc has a very small bevel (1 or 2 degrees) that allows you to grind bigger blades without contacting the other side of the disc when you cross the center. This creates a very, very small concave/hollow grind effect.

--nathan
 
marekz said:
what is the advantage of having a beveled disc versus a flat disc.--thanks marekz http://www.beaumontmetalworks.com/index.html
Click to expand...

I'll take on that part of the question because I've been through it recently.

The idea of the bevel is that your blade only touches one side of the disc at a time preventing the tendency to 'spin' the workpiece if the part passes centre of the disk.

The problem with it is that the bevelled disc is actaually a cone without a flat spot on it anywhere. It is a very low cone, but to envision the problem, think of a higher cone and trying to flat sand something on it.

I understand the bevelled is great for working toward mirror finish etc, but I wanted my disc for flattening tangs, scales and bolsters. The flat one was called for. The other really sweet things about Rob's discs are the 8 7/8 diameter (so you can easily trim 9 x 11 sheets) and the heavy, well balanced construction.

Rob!
 
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OK Guy's , help my small brain visualize this :jerkit:. Both Nathan and Rob say the disc is not a true flat . I see it as flat from the edge to the center . Basically the edge of the disc would be .0001-.0002 of an inch thinner than the center . A computerized lathe could cut this , leaving a true flat area from the center to the edge . I've read this many times and my poor brain gets confused each time . :D
 
Jack, you are correct. The disc from center to edge in any given direction would be true flat at that exact, finite ray. Think of it this way. If you placed a pice of wood on the disc, horizontal with the ground (for a vertically mounted disc) and even with the center, the very center of the piece of wood would be ground true flat. From the center moving towards the upper and lower edges of the scale would actually be a very shallow hollow.

Basically, once you hold one of these discs in hand, you'll see it right away once you put material on it. If you take a large rectangle of micarta and place it on the disc, it will act like a see-saw with the very center being the fulcrum. That very center fulcrum will be truly flat and make contact through the entire length of the micarta center from center to edge of the disc, but on either side, the disc will slightly drop away.

Hope that makes sense. :)

--nathan
 
Thanks Nathan , I see what you are saying . I don't see that as much of a problem depending on how one grinds his/her blades .

PS. How do you like yours . I've always wondered if you kept the rubber and plexiglass on it or not .
 
DOPE! For some reason I just posted not even thinking that I bought the dang disc from you in the first place! Sorry :o. It's been a long week. I graded student practicals for 11 hours yesterday, and I'm a bit numb today.

I haven't actually mounted and used the disc yet. I left the rubber and plexiglass on and will keep it that way until I get a chance to use it to see if I like it. I almost bought a motor on Monday for the thing, but held off thinking, "I need more power!" :D I'm keeping an eye to the ground for an ~1800 rpm 1.5-2 hp motor, and I'm going to wire up a switch to my existing 2hp vfd to control it. If I don't end up getting a motor, I'll have to build a tooling arm mount for my KMG.

Hopefully, I'll get it mounted by the end of the year. I'm hesitant to spend more this month until I get past the Christmas spending.

--nathan
 
It must just be me Nathan , I read from almost everybody here that they need more power . Since the early 90's I have been running my 2x72 on a 3/4hp 1725 rpm open motor , belt driven with 4 step pulleys and have never stalled that motor or burned it up , my contact wheel is the drive wheel if that makes a difference , and my disc is a 1/3 h.p 1140 rpm open motor and both were used motors off the shelf from work . Guess I've been lucky . Someone once called me a Zen grinder plus at my age , load noise and speed scare me :D
 
I have the flat disc and if you put the blade at a 45 degree angle and hold just below center you get about 7'' of flat grinding. My disc runs on a Leeson 1hp 3ph and does great, it's a finesse tool not for hoggin', don't think the bigger motor is neccessary.
silver_pilate said:
Horizontal grinders would be great for edge finishing and other detail work. A disc grinder works great for finessing and finishing blade bevels and establishing true flats, and I've heard of a few makers who have made knives start-finish soley on a disc.

A flat dist of 9" diameter means that the longest length you can grind easily is 4.5" Anything longer than this, and you cross the center of the disc. That means that you have one side of the knife in which the paper/grit is going down while at the same time, on the opposite side, the paper/grit is going up. This creates a rotational moment in your work and makes it very hard to easily control the blade. However, flats are truly flat with a flat disc.

A beveled disc has a very small bevel (1 or 2 degrees) that allows you to grind bigger blades without contacting the other side of the disc when you cross the center. This creates a very, very small concave/hollow grind effect.

--nathan
Click to expand...
 
Haha...I hear you, Jack and Mike. Maybe I just need to suck it up and buy the cheap 3/4 1750 rpm 3phase from Grizzly and get in touch with my zen. My history includes hot-rodding Mustangs, so the quest for more power and kind of built in. :D

Did you have any trouble at all with that 1/3 hp motor? My use for the disc will really be to true-up grinds and finishing work, so I bet 3/4 hp would be fine. I just have to convince my man-beastliness of that ;).

--nathan
 
silver_pilate said:
Haha...I hear you, Jack and Mike. Maybe I just need to suck it up and buy the cheap 3/4 1750 rpm 3phase from Grizzly and get in touch with my zen. My history includes hot-rodding Mustangs, so the quest for more power and kind of built in. :D

Did you have any trouble at all with that 1/3 hp motor? My use for the disc will really be to true-up grinds and finishing work, so I bet 3/4 hp would be fine. I just have to convince my man-beastliness of that ;).

--nathan
Click to expand...

Nathan , it was a Baldor motor shop that set me up years ago with the 1/3 hp and low 1140 rpm . I dealt with them for 16 yrs. when I had to work for food . It is a continues torque issue if I remember correctly ( could be wrong ) but I always stalled out the 1725 rpm , 1/2 hp . This was before any suppliers sold any and funny as it might be , true grit came out with a Baldor 1/3 hp at 1140 rpm a couple yrs. later . It may be too slow for some( I'm in no hurry ) but I get many more passes before the heat builds up . I bought a 1 hp 1725 for the disc you bought from me , one pass and it was too hot to hold , plus I can hear my lousy singing to myself :D

In 1980 , I built a 66 2x2 fastback into a Shelby . Full package , moved and lowered the front A-arms, changed rear suspension and rear end 3rd member . Close ratio 4-speed and a hi-po 289 . The work was not fun but sure was to drive until I crashed it .
 
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I wonder if the 1750 rpm motor would behave when slowed down a bit with a VFD. I'm just afraid of losing too much torque if I drop it down to, say, 1/2 speed or about 900 rpm.

That sounds like a nice little pony, Jack. I rebuilt the motor in my 91 GT 5.0 twice. The first was into a 306 with Dart windsor heads and 10:1 compression and a nice, lopey cam. I added full intake and exhaust package. I ran the dog AOD tranny, but I rebuilt it with a custom valve body for full manual/automatic control and better life out of the OD. With 3.73 gears, it shifted like God kicked it in the bumper. The second rebuild was into a 347 stroker with bullet proof rotating assembly. I stuck with the intake/exhaust and upped to bigger injectors. Sure was fun to drive: bright red with all black interior. But like you, every time I crawled under the car I remembered how much I hated to actually do the car work. :D

The mustang was parked outside my house one night about 3 years ago, and a drunk driver hit it and pushed it up over the curb. Tore the front suspension out of it and bent the frame all to heck. I didn't have the money to fix it, so I totaled and sold it to my buddy who helped me build it.

--nathan
 
I have the Leeson 1hp 3ph and run it at half speed most of the time. It has never bogged down. I have used a friends baldor DC disc and was very disappointed it took very little to bog it down.
 
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