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How to flatten the sole of a jointer plane

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Forum topic by LJackson posted 04-26-2015 09:47 PM 1925 views 0 times favorited 21 replies Add to Favorites Watch
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LJackson

295 posts in 1059 days


04-26-2015 09:47 PM

I purchased a Faithfull number 7 jointer plane, and I expected that I would need to flatten it. So, I went to the box store and bought a 3/8 inch thick piece of glass that is about 24”x12”. It is normally used as a glass shelf. I have glued 80 grit sandpaper to it and proceeded to run my plane across it for quite some time, and still haven’t gotten the entire sole ground.

I’m pretty sure now that this piece of glass isn’t truly flat. I think it bows in the middle. I am not sure how I can be 100% certain of this. I have taken a couple of “straight” edges and they all seem to agree that there’s a bend to the glass. But, without having a known “perfect” straight edge, I do not know how else to verify the flatness of this piece of glass. I assumed it would be flat due to the nature of its manufacture.

I think it would be prohibitively expensive for me to buy something like a Starrett 24” engineer’s straight edge for this purpose. I have thought about somehow stretching fishing line between two points, as that is assured to be straight, but then using such a thing to confirm or deny that something else is straight or flat eludes me; if it touches the surface, it will bend around any irregularities, and so must be kept just a fraction above it.

So, now I’m stuck. I do not know where I can get a known true flat reference of about 24” in length which I can use to flatten the sole of my plane, and I do not know how I can verify that such a surface is truly flat.


21 replies so far

View ColonelTravis's profile

ColonelTravis

1192 posts in 1359 days


#1 posted 04-26-2015 10:20 PM

Look for a cabinet shop near you. They throw away granite all the time, some of them will give you a piece for free because it’s one less piece to haul away. I got one that was a sink cutout, it’s a little under 3 feet long and perfect for flattening plane bottoms.

Flattening a jointer is boring as hell and will take forever. It’s probably the only thing in woodworking I truly hate. But after doing it once I’ll most likely never do it again. When I flattened my #8 I didn’t start with 80 grit sandpaper. I started with a 40 grit sanding belt.

Also, if you have a hollow in the middle-back of your plane behind the mouth (not right behind the mouth) and it’s not a trench, it’s most likely fine. Toe, mouth, heel – these areas need to be flat. I like the sides flat (sides of the bottom, not the side of the plane) but a back-middle hollow? Screw it.

View Bill White's profile

Bill White

4456 posts in 3426 days


#2 posted 04-26-2015 10:24 PM

Go to You Tube and check out David Weaver’s vid on plane lapping. It will be time well spent.
Is your bench flat?
Bill

-- bill@magraphics.us

View waho6o9's profile

waho6o9

7174 posts in 2042 days


#3 posted 04-26-2015 11:25 PM

https://www.youtube.com/watch?v=RVy789Oxq98

Thanks for the friendly advice Bill, it’s definitely worth a listen.

View Don W's profile

Don W

17969 posts in 2033 days


#4 posted 04-26-2015 11:34 PM

Are you trying to flatten it because you think you should, or because the plane isn’t working correctly.

-- Master hand plane hoarder. - http://timetestedtools.net

View Dan658's profile

Dan658

93 posts in 735 days


#5 posted 04-27-2015 12:49 AM

I’m not saying you should do this, but I had a block plane that had a sole shaped like a banana and I got sick of rubbing it on stones, so I took it to my bench top belt sander. I made sure not to let the metal get too hot and it worked out well for me. Once I got it flat on the belt, I went back to the stones and finished it off. A little unconventional, but it worked for me.

View Dan658's profile

Dan658

93 posts in 735 days


#6 posted 04-27-2015 12:51 AM



I m not saying you should do this, but I had a block plane that had a sole shaped like a banana and I got sick of rubbing it on stones, so I took it to my bench top belt sander. I made sure not to let the metal get too hot and it worked out well for me. Once I got it flat on the belt, I went back to the stones and finished it off. A little unconventional, but it worked for me.

- Dan658

And somehow I over looked the fact that you are working with a #7 rather than a block plane like myself. So yeah…...

View TheFridge's profile

TheFridge

5765 posts in 951 days


#7 posted 04-27-2015 01:06 AM

Picked up a couple scrao pieces of 3/4-1” granite and I’m surprised how flat it is. An extruded aluminum straight edge and a set of feeler gauges will tell you all you need to know. Extruded aluminum is generally considered to be pretty damn straight. It’s worked for me.

-- Shooting down the walls of heartache. Bang bang. I am. The warrior.

View Tim's profile

Tim

3119 posts in 1427 days


#8 posted 04-27-2015 01:07 AM

I m pretty sure now that this piece of glass isn t truly flat. I think it bows in the middle. I am not sure how I can be 100% certain of this. I have taken a couple of “straight” edges and they all seem to agree that there s a bend to the glass. But, without having a known “perfect” straight edge, I do not know how else to verify the flatness of this piece of glass. I assumed it would be flat due to the nature of its manufacture.

I think it would be prohibitively expensive for me to buy something like a Starrett 24” engineer s straight edge for this purpose. I have thought about somehow stretching fishing line between two points, as that is assured to be straight, but then using such a thing to confirm or deny that something else is straight or flat eludes me; if it touches the surface, it will bend around any irregularities, and so must be kept just a fraction above it.

So, now I m stuck. I do not know where I can get a known true flat reference of about 24” in length which I can use to flatten the sole of my plane, and I do not know how I can verify that such a surface is truly flat.

- LJackson

I’m no machinist, but I was really curious about this so I read up on it. Basically you take 3 straightedges and check them against each other flipping one end for end, then check against another, making 6 combinations. 2 aren’t enough because there are shapes where two can fit inside each other like spoons. This is also how you lap straightedges to get a perfect straightedge without having a reference to start with. Check 3 against each other, mark the high spots, remove a little, check again, etc. There’s more to it, but that’s the basics.

View LJackson's profile

LJackson

295 posts in 1059 days


#9 posted 04-27-2015 10:32 AM

Don W, I thought that was what you do when you first buy a new hand plane, particularly one that doesn’t cost $400. I’ve also read that folks who purchased a Faithfull have done this.

Now, of course, having run it across an unflat surface, I’m sure it isn’t flat, if it ever was.

Tim, thanks for that tip. I will look into it more. That makes sense.

View Don W's profile

Don W

17969 posts in 2033 days


#10 posted 04-27-2015 12:02 PM

My next question would be what did you set the glass on. Typically you glue the glass to some flat substrate. Glass will flex.

Also what does the straight edges tell you on the bottom of the plane?

If you can tell the plane isn’t flat by running it across a surface, I’m afraid you have your work cut out for you.

If I’m going to resell a plane as tuned, I’ll make sure its flat, because that’s what people have been told, and they believe it. If its one of my users, or I plan to keep it, I try it. If it works, I’m not going to fix what’s not broken.

-- Master hand plane hoarder. - http://timetestedtools.net

View PatrickH's profile

PatrickH

51 posts in 1353 days


#11 posted 04-27-2015 01:09 PM

I would find a friend who has a surface grinder or contact Tablesaw Tom. Flattening a jack with a reasonably straight sole, took forever…I nearly screwed it up. I couldn’t imagine doing a jointer.

-- http://bloodsweatsawdust.com

View rwe2156's profile

rwe2156

2198 posts in 946 days


#12 posted 04-27-2015 01:58 PM

Do you have a tablesaw or jointer?
If so, attach adhesive roll sandpaper.
Start with 80 and 120 grit and go to 220 that’s adequate.
Be prepared for ALOT of work.

If you don’t have a TS, then the granite is your best shot.
Also, a piece of DS melamine is usually flat enough for this.

I wouldn’t recommend machining you’ll have more money than the plane is worth, plus on a plane this big you’ll probably get some warping after machining. The machinist people here can tell you about problems with clamping and surfacing metal this thin.

-- Everything is a prototype thats why its one of a kind!!

View OSU55's profile

OSU55

1059 posts in 1455 days


#13 posted 04-27-2015 03:55 PM

For one, you’re over thinking the straight edge part. About any of the box store carpenter or combination squares have edges straight enough for looking at a plane sole. Put the edge to the sole and hold it up to a light. Here is my sole flattening method.

I advise against paying to have a plane surface ground (unless you can have it done for free) – #1 it’s expensive, #2 it will not be flat – typically the bed will need to stripped of everything, and after everything is bolted back on the sole will assume a different shape, and iron of this size and thickness will move around as it is ground. It’s an ok 1st step if you can have it done for free.

Glass glued to a flat substrate still needs to be supported by a flat surface (does not have to be smooth). If the surface under it is bowed over the length, the glass will flex. The glass or other surface should be 12” or so longer than the plane – if both ends come off the sandpaper as the plane is stroked it will create a hollow. I’ve used granite inspection tables fo sole flattening also, and they are no better than glass on a flat surface. The melamine coated shelving or formica cabinet top, placed on a flat surface, should be flat enough.

View Texcaster's profile

Texcaster

1140 posts in 1139 days


#14 posted 04-27-2015 11:12 PM

LJackson wrote

“I think it would be prohibitively expensive for me to buy something like a Starrett 24” engineer’s straight edge for this purpose. I have thought about somehow stretching fishing line between two points, as that is assured to be straight, but then using such a thing to confirm or deny that something else is straight or flat eludes me; if it touches the surface, it will bend around any irregularities, and so must be kept just a fraction above it. “

I use a string to check my jointer tables for coplanar alignment once in awhile.

Cut a piece of 20mm x 20mm into three pieces. Put a piece of timber at both ends of the machine with a weighted string on top. Use the third piece to check the gap.

-- Mama calls me Texcaster but my real name is Mr. Earl.

View BurlyBob's profile

BurlyBob

3692 posts in 1731 days


#15 posted 04-28-2015 12:33 AM

I got to ride with Colonel Travis. I’ve done everything he said. I just didn’t have anyone to guide me. He’s right to flattening a plane is tedious and boring, but you can have a beer or three while doing it and nothing else!!!!!
I’ve gone only one step further that I can’t recall other LJ’s doing- draw filing the sole.

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