Old Paper Cutter Restoration & Blade Sharpening Question

[JoeLee]

This was another project that sat on one of my benches for probably 20 years. Finally got around to finishing it. My plans are to use it for cutting gasket material and thin plastic and maybe brass shim stock.

A while back I ground both surfaces of each blade. They was some rust and staining. SG cleaned both of them right up. Probably removed about .015 from each, ground them together.

The starting edge of the handle blade is worn pretty bad towards the top where it first meets the lower blade. No way I could grind all that out so I have to live with it.
The starting edge of the lower blade edge where it first contacts the handle blade was worn in about .030 in about 2" down. The result was it wouldn't shear a straight line.
So, the other day I milled the edge of the lower blade straight and finished it up on the grinder. Removed about .032 of the edge in all.

In testing this thing out sometimes it doesn't want to cut at the top edge and sort of folds the paper over, unless I chop it fast.
The lower blade is already showing some signs of a burr forming on the edge from the few times I've played with it.. The edge is ground square and I'm wondering if I should grind a slight relief angle in it?
The handle blade is set at about a 3 deg. angle as shown.
Originally, the edge of the lower blade was just sheared, never ground, it looked like it was tapered but I believe that was just the way the shear cut it.

Any ideas here??

JL....................






JL...........

[mickeyf]

I have a baby one of these that works quite well. On mine, the blades are both appear to be ground with a slight curve when looked at from the end:



Other than the curved faces the other edges look to be dead flat and square (just not in my sketch!). Also, the movable blade has spring tension so that it presses inwards against the fixed blade as it descends.

[JoeLee]

Mickey, There's probably a few different designs then if yours are like hollow ground like you show. Beyond my capabilities in my shop, but mine were dead flat.
Mine also has a spring that puts inward tension against the lower blade. Typical of these from what I've seen.
I probably should have just made a new lower blade. Since I reduced the width by .032 that lessened the tensions between the two. Then I created the problem where I had to file the little nub on the handle where it rides on the pivot mount and I had to file a little on the mating part. That reduced the tension even more. So to compensate I made a .060 washer / space to go between the spring and the nut. That about evened it out by putting back more tension between the blades.

I'm wondering if I should experiment with the lower blade edge angle a little. I can't find any decent pics of these things to see they were actually fitted.

JL...........

[Lew Hartswick]

Is there a Drafting Supply store anywhere you can go look at one ? Take along a good 6" scale and check one out. :-)
...lew...

[reggie_obe]

Have you read through any of the online references?
https://www.hamblyscreenprints.com/h...-paper-cutter/
This one refers to the type used in a printing shop, but might be of help: https://www.papercutters.com/resourc...ide-save-money

[thin-woodsman]

The cutter should be performing a shear cut, just like scissors, correct? I don't believe that changing the angle would improve things - the two edges must be straight and square, though either can have an outer bevel (e.g. on the blade) which might help for thicker materials.

That edge by the hinge is pretty beat up alright. Grinding that square and smooth will throw off the rest of the blade, so you're going to have to grind the enrie blade back the same distance. Once ground back and sqaure, though, it will probably work just fine (albeit with some shims to bring it in contact with the base part of the shear).

[JoeLee]

Is there a Drafting Supply store anywhere you can go look at one ? Take along a good 6" scale and check one out. :-)
...lew...

There used to be a couple places locally but they are long gone. I really miss them.

JL...............

[JoeLee]

Have you read through any of the online references?
https://www.hamblyscreenprints.com/h...-paper-cutter/
This one refers to the type used in a printing shop, but might be of help: https://www.papercutters.com/resourc...ide-save-money

The info in the links don't seem to address my type of cutter and are mostly methods of honing the blade edge rather than grinding. Sharpening them on a bench grinder is mentioned somewhere in one of them. I'd love to see the results from some inexperienced person sharpening them on a bench grinder. I'll have to read it over again.

JL................

[eKretz]

My idea is to grind the top blade the rest of the way to clean-up. Shim it out afterwards if necessary. The item being cut will fold over every time if your blades aren't meeting correctly. There can't be a gap. Does it fold like that in the area where you have crisp ground surface all the way to the edge?

I would also take a very fine stone - something like a black or translucent Arkansas - and carefully stone that burr you mentioned so that you have a crisp edge again.

[JoeLee]

The cutter should be performing a shear cut, just like scissors, correct? I don't believe that changing the angle would improve things - the two edges must be straight and square, though either can have an outer bevel (e.g. on the blade) which might help for thicker materials.

That edge by the hinge is pretty beat up alright. Grinding that square and smooth will throw off the rest of the blade, so you're going to have to grind the enrie blade back the same distance. Once ground back and sqaure, though, it will probably work just fine (albeit with some shims to bring it in contact with the base part of the shear).

Yes, the blades do preform a shear type cut but the contact angle of the two blades is a bit more radical than scissors as you can see by this picture. It's edge against edge and they tend to chew each other up. As I said previously, the lower blade has already developed a slight burr just from the few times I've played around testing it. It won't last long at this rate.

The blades are not very hard, perhaps tempered to a degree. I can file them. They are just sheared sheet metal. The counter sink part of the screw holes is blue in color so that tells me that some heat treat process has been done, the edges are not blue. Maybe these were tempered, stamped out and then finish ground ?

As far as the starting edge of the handle blade, no way I'm going to grind all of that blade to remove the hack up end. I would have to remove over .025 to clean that up.
I may just polish it smooth. As along as it';s sharp and contacts the lower blade it will still cut. As long as the lower blade is straight my paper cut will be straight.



Here is a sketch of how the blade angles meet. The top drawing is how they are now. I ground the lower blade edge square.

My other option is to grind a slight relief angle in it as shown in the lower sketch. By doing that it will just about put the two blade edges on the same plane and reduce that edge to edge contact. If it doesn't work out I can always grind it back square again.
Originally, the lower edge looked like it had a slight bevel to it but as I said it was just a sheared edge and sheet metal shears have a tendency to cut that way.





JL.....................

[eKretz]

The relief angle may help a little. Most shears I've used have a slight relief on the bottom blade, whether it's from an angled grind or that the blade is mounted at a slight angle.

The top blade's worn area will probably not cut well no matter what you do *unless you grind it out.* It is approaching the work at a negative angle, which is going to make it want to push rather than cut. Either start your cuts farther down the blade or grind it out. And your blade is almost certainly tempered, but to a much softer level of hardness than something like a metal shear.

You've said this twice already, but I would be shocked if that bottom blade edge were sheared from the get-go. I don't think so, unless it was made somewhere like China. What you're probably seeing is heavy wear or a coarse grind. Did you regrind that edge also? If not, you absolutely should have.

[JoeLee]

I filed and polished out the front edge of the blade and blended it in. Gave it a try. It now shears right from the very top where the blades start to come in contact. That's well before where it will normally start when the ruler is in place. There needs to be some sort of a leading or starting edge anyway. If the handle is raised to vertical the blades no longer touch with out the leading edge they would crash. It still cuts straight because the straightness of the cut is determined by the straightness of the lower blade edge. It now shears fine strips without any issues.



I put a couple strips of paper shims .011 in total thickness under the inside edge of the lower blade to mimic a relief angle. That made it cut much smoother and eliminated the grating sound when shearing. It made for a smoother blade contact. So now I'll set the blade up on the grinder and grind in the relief angle. Should be good to go for many years.



JL................

[Beazld]

If it works it’s right! Nice job Joe!

[JoeLee]

I had to play around with a couple different thickness shims to get the desired 3 deg. or so relief. Ended up sticking .010 thick shim strips along the edge of my magnetic transfer blocks.
Set the blade up against it and ground the relief angle on the edge.
Worked out perfect.

JL..................

[JoeLee]

This is what the blades looked like originally. The cutting board was in 3 pieces when I got it. Can you tell where the glue joints are??

JL.....................