Thread: Setting jointer knives - tolerances?

Hi Dengue I would say your tolerances are fine.
The knives need to be slightly higher then the outfeed table, if you set them below then timber will catch on the outfeed table.
You will get a tiny bit of snipe on the back ends,but can be got rid of at the thicknessing stage.

Originally Posted by mark david

Hi Dengue I would say your tolerances are fine.

No problems at all there, I agree.

The knives need to be slightly higher then the outfeed table, if you set them below then timber will catch on the outfeed table.

Thanks for that Mark, makes a lot of sense.

No matter what the tolerances between the plane of the outfeed table and the top of the knives at Top Dead Centre, all the tolerances must be the same for each knife. Within 0.5 thou? Otherwise you get one blade doing all the cutting. This is proving very hard to do. The Hafco P-200J I am working on has two little Allen keys ( jack screws) under each knife to set the blades level, but the problem is when the 4 gib bolts on each knife are tightened, the height of the knife tends to change, and I cannot work out why.

Easy enough to raise and lower the outfeed table once the knives are all set level.

Originally Posted by Dengue

but the problem is when the 4 gib bolts on each knife are tightened, the height of the knife tends to change, and I cannot work out why.

Take the gib bolts out and flatten their heads on some wet and dry, or file if necessary, then fine wet and dry. You wil find that it is friction from a high spot on the heads of the bolts (off centre) as they are tightened is what is causing the movement. get them as flat and smooth as possible.

Cheers

Doug

Set them in the head pretty close to each other. Dont stress too much about it, if they were within 0.1mm thats pretty good. Then once u have that done, set the outfeed fence to the highest knife. Joint a board, check for leading or trailing snipe and fine tune the outfeed to suit. No snipe should be evidence of a straight board....if the infeed and outfeed tables r parallel. U can get a snipeless board when the infeed and outfeed r not parallel, but u will be making bananas.

I used to have a Kity combination machine way back in the 1980's and think the same happened to me, as soon as I tightened the bolts the blade rose up.
I suspect this may be a common problem.
Are you using a knife setting jig?.

I upgraded to a spiral head just over a year ago so no longer have the issue.

Originally Posted by Dengue

Thanks for that Mark, makes a lot of sense.

No matter what the tolerances between the plane of the outfeed table and the top of the knives at Top Dead Centre, all the tolerances must be the same for each knife. Within 0.5 thou? Otherwise you get one blade doing all the cutting. This is proving very hard to do. The Hafco P-200J I am working on has two little Allen keys ( jack screws) under each knife to set the blades level, but the problem is when the 4 gib bolts on each knife are tightened, the height of the knife tends to change, and I cannot work out why.

Easy enough to raise and lower the outfeed table once the knives are all set level.

Before we went helical at work our tolerance was 0.5 thou
Took some time to set, but never had snipe or uneven finish

As Doug says the contact face of the bolts are not truly flat or the bolts are not truly straight or perhaps they are moving around in the thread in the head during the tightening process.

Originally Posted by elanjacobs

Before we went helical at work our tolerance was 0.5 thou
Took some time to set, but never had snipe or uneven finish

I bet it took some time to set. what did you do? tap the blade into place with a wet feather?

Cheers

Doug

You wil find that it is friction from a high spot on the heads of the bolts (off centre) as they are tightened is what is causing the movement. get them as flat and smooth as possible.

Thanks for this doug, will give it a go

Found another forum thread which expressed the same problem

Spent all yesterday trying to set up the 4 blades on my HafCo P-200H jointer, without success.

Today I started again, this time flattening the heads of the gib bolts on the holding bar. You could see where each bolt had been turning on the off-centre highspots to tighten the blades in position, one of the main reasons for the blades to rise on final tensioning, as advised by doug3030 above. This work certainly removed a lot of the random, unpredictable change in blade height that I experienced yesterday, but did not eliminate it. I think that I should have made the gib bolt head into a dome shape to further improve or even eliminate this common problem. I was subsequently able to have a fair guess at just how much the blades would rise in the final tensioning, and make allowance for it.

Last night I read the web article here on how to set up jointer knives. I also read the article from Fine Woodworking website here on the Tage Friid method using a board movement to set the height of the blade, and combined the two as follows:

From these articles, I first decided that with the knife at the correct height, it should pick up a 20mm wide test stick when rotating and carry it for 5mm. If all the knives did this, then they would be at the same height, and would protrude above the outfeed table by just the correct amount. Using the calculations in the article with this dimension and the dimension of the cutter head, it turned out a 0.003" height of each knife above the outfeed table would give the right height to carry the board 5mm. It was just co-incidence that I selected this figure, as shown in my original post above.

There was a 4 stage iterative process to be followed to get the blade height right:
1. Fit the blade and tighten snugly with the gib bolts, then adjust the two jack screws under each blade to get the 0.003" correct height of each end of the blades, as measured with a dial indicator. Note the knife edge height above the outfeed table level.
2. Carefully tighten up the gib bolts, a 16th of a turn and then doing the next bolt, working from the centre to the outside very slowly and with even tension on each bolt
3. Note the height of the knife once the gib bolts are fully tightened, and work out how much it has jumped from when it was snugly tightened.
4. Re-do the above steps, but this time set the blades at a lower level to allow for the increase in height once the gib bolts are tensioned to their final tightness

End result was that after another 4 hours work today, the height of each end of the blades was 0.003" to 0.004" above the outfeed table level, and when a 20mm wide test stick was put on the outfeed table, most of the blades carried it for 5mm or so.

Hope this makes sense, and that someone benefits from it. Many thanks for all the contributions above, I really appreciate it

Originally Posted by doug3030

I bet it took some time to set. what did you do? tap the blade into place with a wet feather?

Cheers

Doug

The blades didn't sit directly on the screws, but on a metal cylinder with a flat step milled in it that had an adjusting screw through the middle that was accessible while the blades were in the head. Made fine adjustment rather painless. I could normally get all 3 blades set in 20 mins.

We also have a larger version of this dial gauge which made checking easy

Hi Dengue, to be honest I had forgotten what a complete PITA this can be to set up.
Fortunately I got rid of my last 2 benchtop machines before they needed to be resharpened, so, someone else inherited that headache.

I must confess a few weeks ago I did something that might seem quite crazy.After using all four edges on my carbide inserts for the helical head,I took every one out and resharpened every single one by hand, I lapped each one 100 times on a diamond stone all 65 of them! And put them back in, They were virtually as good as new.Certainly no problems are evident with the cuts I am getting.
Certainly beats paying Carba-tec about $500 for a new set They can be bought on the internet for about $2.50 each but couldn't be bothered with the hassle.


All in all probably took a couple of hours but was certainly worth the effort
1

Originally Posted by Dengue

Spent all yesterday trying to set up the 4 blades on my HafCo P-200H jointer, without success.

Today I started again, this time flattening the heads of the gib bolts on the holding bar. You could see where each bolt had been turning on the off-centre highspots to tighten the blades in position, one of the main reasons for the blades to rise on final tensioning, as advised by doug3030 above. This work certainly removed a lot of the random, unpredictable change in blade height that I experienced yesterday, but did not eliminate it. I think that I should have made the gib bolt head into a dome shape to further improve or even eliminate this common problem. I was subsequently able to have a fair guess at just how much the blades would rise in the final tensioning, and make allowance for it.

Last night I read the web article here on how to set up jointer knives. I also read the article from Fine Woodworking website here on the Tage Friid method using a board movement to set the height of the blade, and combined the two as follows:

From these articles, I first decided that with the knife at the correct height, it should pick up a 20mm wide test stick when rotating and carry it for 5mm. If all the knives did this, then they would be at the same height, and would protrude above the outfeed table by just the correct amount. Using the calculations in the article with this dimension and the dimension of the cutter head, it turned out a 0.003" height of each knife above the outfeed table would give the right height to carry the board 5mm. It was just co-incidence that I selected this figure, as shown in my original post above.

There was a 4 stage iterative process to be followed to get the blade height right:
1. Fit the blade and tighten snugly with the gib bolts, then adjust the two jack screws under each blade to get the 0.003" correct height of each end of the blades, as measured with a dial indicator. Note the knife edge height above the outfeed table level.
2. Carefully tighten up the gib bolts, a 16th of a turn and then doing the next bolt, working from the centre to the outside very slowly and with even tension on each bolt
3. Note the height of the knife once the gib bolts are fully tightened, and work out how much it has jumped from when it was snugly tightened.
4. Re-do the above steps, but this time set the blades at a lower level to allow for the increase in height once the gib bolts are tensioned to their final tightness

End result was that after another 4 hours work today, the height of each end of the blades was 0.003" to 0.004" above the outfeed table level, and when a 20mm wide test stick was put on the outfeed table, most of the blades carried it for 5mm or so.

Hope this makes sense, and that someone benefits from it. Many thanks for all the contributions above, I really appreciate it

Originally Posted by mark david

Hi Dengue, to be honest I had forgotten what a complete PITA this can be to set up.
Fortunately I got rid of my last 2 benchtop machines before they needed to be resharpened, so, someone else inherited that headache.

I must confess a few weeks ago I did something that might seem quite crazy.After using all four edges on my carbide inserts for the helical head,I took every one out and resharpened every single one by hand, I lapped each one 100 times on a diamond stone all 65 of them! And put them back in, They were virtually as good as new.Certainly no problems are evident with the cuts I am getting.
Certainly beats paying Carba-tec about $500 for a new set They can be bought on the internet for about $2.50 each but couldn't be bothered with the hassle.


All in all probably took a couple of hours but was certainly worth the effort
1

Feel like sharpening our carbide tips as well? Only 376 of them