Aligning jointer knives with magnets

[Mike in Idaho]

Hello,

I spent the weekend tuning up my shop and I purchased a the polycarb jointer jig with magnets from Woodcraft to reset my knives. I have a Sunhill jointer (like Jet/Grizzly, etc) and the knives are held in place with a magnet piece that has screws that bind the knives/magnet into place in the cutterhead. The two pieces sit on a couple of springs (I assume to help align the knife).

One thing I noticed is that the springs were so strong that the knife assembly pushed up on my magnet jig. So I ended up lining up the jig first (on TDC - true dead center) and then putting a block on top of the jig to hold it down, sliding the knife assembly underneath so the tip of the knife lined up with the mark on the jig and then secured it.

Once I installed all 3 knives I did the board slide test (as described in the archives). I put a mark on the board, set the board on the outfeed table, over the cutterhead as well, and lined the mark up to the end of the table. As I rotated the cutterhead (using the belt) I found that one knife moved it about 1/8", the 2nd knife about 1/16" and the third just barely touched it. Oh, I should probably point out that I aligned the outfeed table to the first knife before checking the other three (hoping they would match). So at this point I do get nice flat boards when run through the jointer, but logic says one of my knives is working harder than the other 2.

So, since I'm not really using the magnets to set the knives (I have to push down on the jig to keep the springs from pushing the jig up), it's acting as more of a flat hold down. Ugh.

Here's my question: Is it possible to remove the springs without affecting the performance of the jointer? By removing the springs it seems that the jig would perform as it was designed -- to hold the knife assembly UP not push it down -- thus I would be exerting less pressure on the knives and I assume I would be able to align them more precisely.

Or do I just keep aligning them over and over until they match with the push test? I'm I dreaming that that's possible?

Thanks, Mike

[T Clapp]

I think you didn't need to buy the magnet. The springs do the same thing...keep the blade pushed up against an object that is flush with the outfeed table. You put a straight steel rule on the outfeed table and let the blade touch it at specified distance from the edge of the outfeed table which represents TDC. You're probably right, though...since ya already spent those bucks, can remove the springs if you want.

Did you plane a board yet? I can usually tell if the blades are alligned just by the nice smooth sound of the machine. Unalligned blades make more noise and vibration even when newly sharp. The board test is not always accurate since the blade can slip on the board a bit .

[Brian in Vancouver, BC]

I have had my jointer for about 3 months now and have not yet had to change the blades. When do you decide it's time to make a change (replace/flip them)? About how much wood does a blade handle (feet of material)? I realize that the hardness of the material will make a difference. I am using Ulmo (sp?) which is softer than maple I believe. Do I look for certain marks or shininess on the surface?

Brian

| > I spent the weekend tuning up my shop and I purchased a the polycarb | jointer | > jig with magnets from Woodcraft to reset my knives. I have a Sunhill | > jointer (like Jet/Grizzly, etc) and the knives are held in place with a | > magnet piece that has screws that bind the knives/magnet into place in the | > cutterhead. The two pieces sit on a couple of springs (I assume to help | > align the knife). | >

| > One thing I noticed is that the springs were so strong that the knife | > assembly pushed up on my magnet jig. So I ended up lining up the jig | first | > (on TDC - true dead center) and then putting a block on top of the jig to | > hold it down, sliding the knife assembly underneath so the tip of the | knife | > lined up with the mark on the jig and then secured it. | >

| > Once I installed all 3 knives I did the board slide test (as described in | > the archives). I put a mark on the board, set the board on the outfeed | > table, over the cutterhead as well, and lined the mark up to the end of | the | > table. As I rotated the cutterhead (using the belt) I found that one | knife | > moved it about 1/8", the 2nd knife about 1/16" and the third just barely | > touched it. Oh, I should probably point out that I aligned the outfeed | > table to the first knife before checking the other three (hoping they | would | > match). So at this point I do get nice flat boards when run through the | > jointer, but logic says one of my knives is working harder than the other | 2. | >

| > So, since I'm not really using the magnets to set the knives (I have to | push | > down on the jig to keep the springs from pushing the jig up), it's acting | as | > more of a flat hold down. Ugh. | >

| > Here's my question: Is it possible to remove the springs without | affecting | > the performance of the jointer? By removing the springs it seems that the | > jig would perform as it was designed -- to hold the knife assembly UP not | > push it down -- thus I would be exerting less pressure on the knives and I | > assume I would be able to align them more precisely. | >

| > Or do I just keep aligning them over and over until they match with the | push | > test? I'm I dreaming that that's possible? | >

| > Thanks, | > Mike | >

| >

| |

[Mike in Idaho]

In my case (I've only been woodworking for 1.5 years) I was stupid enough to run some MDF on my jointer. Since then I've learned that not only are there harsh glues in MDF you also get bits of rock and other crap. Ugh.

Needless to say I have some minor (they are minor) nicks in my knives now -- very easy to see on the wood, you get nice little inverted grooves (probably

2 thou. wide is all -- but they're visible). I was trying to slide one of my knives perpendicular to the tables (sideways I guess you could say) so that the nicks no longer line up and hopefully remove some of the grooves as a result.

Mike

[Mike in Idaho]

Thanks, good point. In fact, since I have access to a machine shop I probably could have made a nice flat aluminum bar with cuttouts for my wrench, but ah well -- I only spent $30. I'll have to try removing the springs and see if that makes it easier.

Although, if one blade is more proud than the others, technically speaking it should wear faster and eventually be in line with the other 2 anyway...

Mike

[Bridger]

nope. it'll just get dull faster and thump the wood even harder....

[Mike in Idaho]

Mmmm...good point. Guess I'll go back and realign them again.

Mike