Thread: Setting jointer knives - tolerances?

Originally Posted by Dengue

Just found this YouTube video by Rob Vaughan showing much the same method as I used. The difference in height that he found after fully tightening each blade was about 0.002". I found the same, or less.
The difference between his method and mine is that he ends up with the blades level with the outfeed table, whereas I end up with the blades between 0.003" and 0.004" above the outfeed table.

Which do you think is preferable? With them level, and with the blade eventually wearing, the front edge of the timber being processed will then hit the front edge of the outfeed table, as Mark posted above.

I was taught to set level with the outfeed table. If the blades get worn enough to cause the timber to hit the edge of the table you should probably be sharpening them more often

Hi thanks for the generous offer but think I'll pass.
I am however travelling to England in May so might need to keep myself occupied for the 18 hours

Originally Posted by elanjacobs

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

I was taught the same method as the 5mm markings on a straight stick. I prefer to use 3mm markings, I dont know what an exact measure that works out to be, but it works. This will leave the knives slightly above the outfeed, if I use a micrometer to measure it, it would read "half a bees willy". Set it so it works for u, higher above the outfeed will make it easier to move large, heavy timbers over the jointer, but too high leaves trailing snipe.

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

You have got more patience than me. The bolt heads are not remaining concentric to their axis so either they are moving about in the thread they tighten on or the bolts are slightly bent which seems unlikely. perhaps using a different style of allen key might help as short bent style keys usually encourage the user to move the tool about and pull the bolt head around if you follow what I mean. Another fix might be to concave the bolt heads slightly so only the circumference of the bolt contacts the blade, a lathe would be needed for this. Have you seen the glass and rare earth magnet trick? Put a sheet of glass over the blade and rare earth magnets on the top of the glass to pull the blades up to the underside of the glass and tighten the bolts. The gibs to lift the blades do nothing in the end and you could give them the heave over your shoulder.

This would have to be the best thread I have ever read on any forum for anything to do with machine setup.

It is great not only for the result - Dengue's excellent step by step instructions for doing it - but also for everyone contributing their knowledge and resources.

This should be put somewhere where it is easy to find next time someone needs it. What a great resource it would be if we had a guide like this for every machine in the workshop. If we did, it would probably improve everyone's woodworking because we would be more wiling to pull things apart to sharpen and fix if we knew we could rely on this quality of support every time.

A big thanks to all who have contributed to this thread, especially Dengue, for pulling it all together.

Cheers

Doug

A simpler method which will arrive at the same place is lay a sheet of glass on the table over the knife to be set and put rare earth magnets on top to draw the knife up to the underside of the glass then tighten the gib bolts. Ignore the height bolts or remove them entirely as using this method they achieve nothing. Do the above for each knife and all the knives will be the same height. Now either using the dial gauge or the timber movement method set the height of the outfeed table to achieve the knife height you want. In the end it is a case of running timber across it and doing fine adjustment on the outfeed table to ensure an even cut along the length of the timber. Once you have that remeasure the knife height and tattoo the setting on the back of your hand never to be forgotten. Of course you could write it in the machine in felt pen which might be a better idea than the tattoo.

Hi Chris, this method is normally used for spring loaded blades, and works well with the springs forcing the blade up against the glass, but it does not take into account the blade slot in the cutter head being forcibly expanded as the bolts are tightened, and the resulting upward movement of the knife. It differs for each slot, and depends on the condition of the gib bolt heads, and the flatness of the gib holding bar against the knife blade.

In the end, with the heads of the gib bar bolts flattened, and the gib bar itself flattened on the surface that holds the blade, you minimise any shift to a predictable level. I went over mine again today after flattening the gib bars, and was able to set the blade 0.001" below the required setting while the blade was snug, before tensioning it up evenly to the final level. In the end each blade was between 0.003" and 0.0035" above the reference outfeed table level.

After that was done I raised the outfeed table to the maximum blade height so that the highest part of the blade was level with the outfeed table, as recommended by elanjacobs and others above. Thsi will avoid the possibility of any snipe ( blade too high) or any concave cuts ( blade too low)

Thanks for the kind comments, doug3030. I was just pulling together a lot of reading and research, and received a lot of valuable comments from some very experienced forum members who so graciously shared these experiences and knowledge. When these guys speak, it pays to listen

Originally Posted by Dengue

Hi Chris, this method is normally used for spring loaded blades, and works well with the springs focing the blade up agaisnt the glass, but it does not take into account the blade slot in the cutter head being forcibly expanded as the bolts are tightened, and the resulting upward movement of the knife. It differs for each slot, and depends on the condition of the gib bolt heads, and the flatness of the gib holding bar against the knife blade.

I have a machine that has spring loaded blade setting against a jig and the jig references to the out feed table all in one go so I have never had to use the glass method but it seems reasonable to me. I would think if the bolts stay parallel to their axis during tightening and the bolts are truly flat on the contact face then the blade cannot move if held by strong magnets. Have you found this not to be the case? If it is a myth then we may as well bust it here and now and save some one a lot of trouble further down the track.

Chris, the more reading and research I do, many say that this knife shifting on final tensioning of the gib bolts is the main cause of pain and frustration setting knife blades. Some even confirm my findings that sometimes it is just the one bolt tightening that throws it all out. It can be quite random and inconsistent. I have also found that as you tension up the blade, one end might increase in height just a small amount, the other end of the blade moves a lot.

By flattening the heads of the gib bolts ( making them a dome shape would be best) and flattening the gib bar itself (see photos below of the gib bar surface before and after flattening) and ensuring no rough or high spots in the slots, you will minimise the height increase, and hopefully make it consistent so you can take it into account. You will always get an increase in blade height as the slot expands, the trick is to minimise this increase and eliminate the random results.


Photo 1: Gib surface after 2 minutes hard work on flattened 240 grit paper
Photo 2: Initial condition of the gib surface that presses against the blade after a few wipes on flat wet and dry paper - this was one of the better ones
Photo 3: Gib bolt heads after flattening on wet and dry 240 grit paper

G'day Dengy,

not or sure if it is me but I can't see any pix just small transparent boxes.

Not sure what is going on there. When I posted the pics it came up with a software Error on line 481, yet I could see the pics. Tried it again just now, same thing, so have left them as attachments. Hope this works

[QUOTE=Dengue;1842240]Chris, the more reading and research I do, many say that this knife shifting on final tensioning of the gib bolts is the main cause of pain and frustration setting knife blades. /QUOTE]

I started to suggest that the bolt contact faces were an issue a few years ago and I have suggested it more than once with no response from those having problems. How did you get them truly flat without using a lathe?

I used the gib bar to hold them vertical, then ran them over 240 grit wet and dry fixed to a flat surface. Worked well. But please don't bother asking the measures of flatness and the variances found on each bolt using this method