I need a bench grinder and there are many to choose from. I think it's odd that on most of the 6" grinders you can't lay a straight edge across the front surface of both wheels without the straight edge hitting the motor housing between the wheels. Only a few have a small enough motor that one could grind a long straight object perpendicular to the wheel and not hit the housing, but those few are of lower horsepower. Is this a big deal when it comes to deburring RV parts with a 6" scotchbrite wheel? Should I get one with the smaller motor or is it not a big deal to be able to grind/deburr an object and hold it perpendicular to the front of the wheel?
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Bench Grinder question
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Vern
Well Known Member
Grinder
Harbor Freight / Grizzley/ Northern Hydraulics all have a grinder/polisher with an extended shaft at a reasonable price. They are better alternatives although many RV's have been built with ordinary bench grinders. I used a drill press to run my scotch bright wheel on my first RV.
Whatever you do, do not grind aluminum on your stone wheels. Explosions can occur.
Harbor Freight / Grizzley/ Northern Hydraulics all have a grinder/polisher with an extended shaft at a reasonable price. They are better alternatives although many RV's have been built with ordinary bench grinders. I used a drill press to run my scotch bright wheel on my first RV.
Whatever you do, do not grind aluminum on your stone wheels. Explosions can occur.
az_gila
Well Known Member
Having the motor body smaller than the 6 inch wheel is a big advantage, if you are buying a new one make sure the straightedge trick works. My grinder is not, and it often bugs me.
I have seen many with smaller motor bodies, such as this straight off the Sears web page...
http://www.sears.com/shc/s/p_10153_12605_00974894000P?mv=rr
I wouldn't worry too much about HP, you shouldn't be doing anything that puts large loads on the wheels.
NOT to use a bench grinder
Diamond,
I suggest you deburr the part by hand with a file. YES, this is a slow process. It takes a few passes with file parallel to the sheet thickness, and a pass or two on each edge at a 45 degree. Going slower however assures you will not F the parts up. You can get things done in a hurry with power, and mess them up about as fast too.
But the main reason NOT to use a bench grinder as you are suggesting is that all the finish marks will be in the EXACT wrong direction from a stress standpoint. Even a scotch-brite wheel will leave marks. Try it and view the results with a 10X loupe. Most parts that have any length, such as doublers and skings should be filed out in the direction of the skin edge, not perpendicular to the skin edge. Any cracks that could form do so across the thin section of the skin (part), due to repeated bending (you wing does flex every flight under at least 1G loads). I'm sure plenty of builders have filed their parts/skins in the opposite direction than I am suggesting. Then again, I am sure there are plenty of builders who have not even filed their skins. And these planes aren't falling out of the sky. But if you're a purist, and don't want to know what the fatigue limit is for your skins, doublers, etc. do it the right way.
Vern has suggested using a drill press, and that will be the CORRECT direction to leave any residual finish (file) marks, since the wheel will be spinning PARALLEL to the skin edge. You still need however to knock off the edge corners (top and bottom) and this is still best done by hand, feeling it with you fingers after small lengths of work (you'll find out pretty quick about what it takes in general).
BTW, do NOT use grinding wheels with aluminum. Some people don't know this, but the wheels will load up with soft aluminum, throw the wheels out of balance, and could come apart.
Diamond,
I suggest you deburr the part by hand with a file. YES, this is a slow process. It takes a few passes with file parallel to the sheet thickness, and a pass or two on each edge at a 45 degree. Going slower however assures you will not F the parts up. You can get things done in a hurry with power, and mess them up about as fast too.
But the main reason NOT to use a bench grinder as you are suggesting is that all the finish marks will be in the EXACT wrong direction from a stress standpoint. Even a scotch-brite wheel will leave marks. Try it and view the results with a 10X loupe. Most parts that have any length, such as doublers and skings should be filed out in the direction of the skin edge, not perpendicular to the skin edge. Any cracks that could form do so across the thin section of the skin (part), due to repeated bending (you wing does flex every flight under at least 1G loads). I'm sure plenty of builders have filed their parts/skins in the opposite direction than I am suggesting. Then again, I am sure there are plenty of builders who have not even filed their skins. And these planes aren't falling out of the sky. But if you're a purist, and don't want to know what the fatigue limit is for your skins, doublers, etc. do it the right way.
Vern has suggested using a drill press, and that will be the CORRECT direction to leave any residual finish (file) marks, since the wheel will be spinning PARALLEL to the skin edge. You still need however to knock off the edge corners (top and bottom) and this is still best done by hand, feeling it with you fingers after small lengths of work (you'll find out pretty quick about what it takes in general).
BTW, do NOT use grinding wheels with aluminum. Some people don't know this, but the wheels will load up with soft aluminum, throw the wheels out of balance, and could come apart.
longranger
Well Known Member
Thanks a lot guys; now I've got something else to worry about
. I never gave any thought to the fact that my grinder's motor is bigger than the wheels. I thought they were all that way. (I do wish I had a deeper throat bandsaw, though...) My bench grinder is getting long in the tooth, so I'll keep an eye out for one with a smaller diameter motor.
I debur anything less than about 4 feet long that isn't a skin parallel to the wheels, and I haven't "F'd up" a part with it yet (that't what hammers and drills are for). For longer stuff, and skins over 0.020, I use a 2" wheel in my die grider. I do resort to the handfile and scotchbrite on 0.020 and 0.016 skins.
Sometimes I think I put the "A" in amateur...
. I never gave any thought to the fact that my grinder's motor is bigger than the wheels. I thought they were all that way. (I do wish I had a deeper throat bandsaw, though...) My bench grinder is getting long in the tooth, so I'll keep an eye out for one with a smaller diameter motor.I debur anything less than about 4 feet long that isn't a skin parallel to the wheels, and I haven't "F'd up" a part with it yet (that't what hammers and drills are for
). For longer stuff, and skins over 0.020, I use a 2" wheel in my die grider. I do resort to the handfile and scotchbrite on 0.020 and 0.016 skins.Sometimes I think I put the "A" in amateur...
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I recently bought this one at Harbor Freight: http://www.harborfreight.com/8-inch-bench-grinder-buffer-94327.html It has a slender motor case. Works great so far.
I got this stand also: http://www.harborfreight.com/universal-bench-grinder-stand-3184.html
I wasn't too happy at first. It vibrated a lot, seemed noisy, and wanted to move around on the floor. I replaced the polishing wheel with a 6" scotchbrite, cranked the mounting bolts down tight, and set it on a cushioned pad. Now all is good.
Jim
I got this stand also: http://www.harborfreight.com/universal-bench-grinder-stand-3184.html
I wasn't too happy at first. It vibrated a lot, seemed noisy, and wanted to move around on the floor. I replaced the polishing wheel with a 6" scotchbrite, cranked the mounting bolts down tight, and set it on a cushioned pad. Now all is good.
Jim
I'm trying to follow your logic here. What if you take all the guards and trays off from around the scothbrite wheel, turn 90 degrees to the front of the grinder and run your edges underneath on the bottom of the wheel so the finish marks are parallel to the edge? Is this the way most folks do this any way?
Buggsy2
Well Known Member
No.
You can spend considerable time overthinking every aspect of the build. Go ahead and do that for a month or two, then just build it.
P
paul mosher
die grinder
Just get a ninety degree die grinder with a scotch bright wheel.
Just get a ninety degree die grinder with a scotch bright wheel.
Very true, but I'm waiting for my tools and kit to arrive, so I'm investing some extra time in shop setup to insure the next 4 years of building are as pleasurable as possible. When the kit and tools arrive, I won't have time to nit pick on things like this, so I'm doing that now.
My MAIN POINT: Keep the file/sanding marks parallel to edges
Diamond,
Sure, you can take the guards off (for use with only the scotch brite wheels, not off course potentially lethal brittle grinding wheels). You can then try to feed vertically up and down smaller parts, up to say 2-3 feet long. Your part of course could never be longer than 2X the distance of the grinder to the floor (allowing for flipping the part around). And even if this was not an issue, I'd like to see someone steadying an 8' long (now tall) skin as they feed the unit vertically, without the skin flopping all over the place. Like Buggsy2 said, you can overthink about any of this. You are doing your homework, and that is admirable. Some of this however has to be experienced. Kind of like you can't become a great violinist by mentally practicing it. Have you thought about how much dust those scotch-brite wheels will kick up all over your tidy little shop? When I hand file the skins, the aluminum dust falls to the floor and I sweep it up. There is a noticeable amount after you have done the full perimeter of a wing skin. If you have a dust collection system, that could minimze dust. Excessive aluminum dust is explosive too (if you pump it though non-explosive proof motors). Google on Apple's supplier Foxconn, as they recently have had some explosions due to all the polishing of iPad cases.
My MAIN POINT was: Keep the file/sanding marks parallel to the length of the part, not across the thickness. How you accomplish this is your business.
On a lesser known but somewhat related topic, here is what happens to pressurized aircraft that experience stress corrosion cracking through lines of rivets. It is what I used to open my A&P sheet metal classes at a local junior college with, to stress how little things matter (the crack started at one or two rivets, and over time unzipped until the top litterally blew off):
http://en.wikipedia.org/wiki/Aloha_Airlines_Flight_243
I know, this was for a pressurized commercial aircraft, but there are some common themes here.
CRACKS LIKE INITIATION SITES, and cracks run across the thickness of sheet metal parts.
Diamond,
Sure, you can take the guards off (for use with only the scotch brite wheels, not off course potentially lethal brittle grinding wheels). You can then try to feed vertically up and down smaller parts, up to say 2-3 feet long. Your part of course could never be longer than 2X the distance of the grinder to the floor (allowing for flipping the part around). And even if this was not an issue, I'd like to see someone steadying an 8' long (now tall) skin as they feed the unit vertically, without the skin flopping all over the place. Like Buggsy2 said, you can overthink about any of this. You are doing your homework, and that is admirable. Some of this however has to be experienced. Kind of like you can't become a great violinist by mentally practicing it. Have you thought about how much dust those scotch-brite wheels will kick up all over your tidy little shop? When I hand file the skins, the aluminum dust falls to the floor and I sweep it up. There is a noticeable amount after you have done the full perimeter of a wing skin. If you have a dust collection system, that could minimze dust. Excessive aluminum dust is explosive too (if you pump it though non-explosive proof motors). Google on Apple's supplier Foxconn, as they recently have had some explosions due to all the polishing of iPad cases.
My MAIN POINT was: Keep the file/sanding marks parallel to the length of the part, not across the thickness. How you accomplish this is your business.
On a lesser known but somewhat related topic, here is what happens to pressurized aircraft that experience stress corrosion cracking through lines of rivets. It is what I used to open my A&P sheet metal classes at a local junior college with, to stress how little things matter (the crack started at one or two rivets, and over time unzipped until the top litterally blew off):
http://en.wikipedia.org/wiki/Aloha_Airlines_Flight_243
I know, this was for a pressurized commercial aircraft, but there are some common themes here.
CRACKS LIKE INITIATION SITES, and cracks run across the thickness of sheet metal parts.
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