Fixturing long workpiece for grinding

I am looking for advice on how to fixture a wood plane in order to surface grind it’s bottom surface flat. The plane is about 20” long and has a very slight convex bow in it. I am guessing it is bowed .002” or so, haven’t measured it yet.

I was thinking we’d get a 1” thick plate as wide as the plane and about 14” long. Grind both sides parallel. Mount it to the plane using the holes that are used for the two handles. There is a single screw hole toward one end of the plane for a handle. There are two more screw holes side by side just behind center that hold another handle. Then for the part that would overhang we’d put a screw jack into the block to provide support.

Place the plane down on its bowed surface on the magnet and shim the two ends so it is as close to flat as possible. Grind the top of the fixture block parallel to bottom of the plane. Flip it over onto fixture block. Grind as much of plane bottom as we can over 15” travel carefully marking the stopping point height on DRO. Rotate the fixture 180 degrees on the magnet and slide the fixture forward and grind the remainder.

Does this seem reasonable? Is there a better fixture or method?

Yes, I know the best method would be to find someone with a longer grinder or to lap the bottom. But we don’t have a flat lapping plate nor do we have a longer grinder.

-Tom

How do you check for flatness without a flat reference
If you have a reference, surface plate perhaps, you can scrape it flat Probbably the fasted way
Bolting it on to something will warp it probably also


Peter

+1 for scraping it (mostly) flat. Actually you don't want the entire base flat, just the throat, front and back end. Less friction, easier to use.

L7

Peter from Holland said:

How do you check for flatness without a flat reference
If you have a reference, surface plate perhaps, you can scrape it flat Probbably the fasted way
Bolting it on to something will warp it probably also


Peter

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Our surface plate isn’t long enough. The person who’s plane it is has a straight edge he believes is a reference. Also no one here has scraped anything before so that isn’t going to work. The instrument maker who uses this plane wants it ground flat as it has been, up until the bow that may have occurred after dropping it...

Use two grinding vises, one near each end. You might need to grind the sides of the plane parallel first.

I’m about to get flamed.....
My old man owns a sawmill, and had a set of 26” planet blades several sharpening shops couldn’t handle (not sure how if all the do is sharpen such things). He handed them off to me. On wood planers, the outer edges never get used so the show the original angle. I put those suckers on the mil, used an indicator on the two outermost edges until it read zero across both and used a face mill with the chip being carried away from the cutting edge of the blades. I planned to hone them in after that but they were sharper than any factory blades for the other planers. We reinstalled them and they cut better than they did when the were new, without ever getting ground.

9finger said:

I’m about to get flamed.....
My old man owns a sawmill, and had a set of 26” planet blades several sharpening shops couldn’t handle (not sure how if all the do is sharpen such things). He handed them off to me. On wood planers, the outer edges never get used so the show the original angle. I put those suckers on the mil, used an indicator on the two outermost edges until it read zero across both and used a face mill with the chip being carried away from the cutting edge of the blades. I planned to hone them in after that but they were sharper than any factory blades for the other planers. We reinstalled them and they cut better than they did when the were new, without ever getting ground.

Click to expand...

How long did they last though?

Luke.kerbey said:

How long did they last though?

Click to expand...

Not sure. They are run a couple days a week and that was a couple years ago. Can’t see why they’d have a shorter life cycle though?
When they dull I’ll just do them again.


Our smaller blades I have made fixtures for so I can run them on the surface grinder. With a sample size of 1, I can’t tell you if it’ll last as long or not, but so far they are holding out great, and the job from setup to finish was a lot easier than it would’ve been on a surface grinder with short travel. I made a fixture for these for the mill while I was at it, that way if they ever need it again, I can do it in minutes.