jig for sharpening planer/jointer blades


Bill Tarbell

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Anyone have a particular style of jig that they like to use for sharpening their long blades?  I like the simplistic function of this store-bought jig by Deulen: http://www.woodcraft.com/Product/152868/deulen-12-jointerplaner-knife-sharpening-jig.aspx but the price is a bit high for my taste ($90).

 

here's a quick pic of it:

152868.jpg

 

 

I was thinking a couple saw kerfs in hardwood would have a similar result and be essentially free.  Possibly with a couple set screws to pin them against the walls like the above jig has.  What do you guys use?

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I bought the jointer knife jig from LV.  It works great on jointer knives, sharpened on sandpaper on a granite plate.  It only take a couple of minutes too.  They sharpen a lot easier than I expected them to before I did it the first time.  I can take the knives off, sharpen them, and reinstall in less than 15 minutes, without getting in a hurry.

 

I expect that wooden jig would work fine.

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I don't know about the portable planer knives but just buying quality knives and sending them out is really going to do a better job. I can see touching up a moulder knife in a pinch but jointer and planer knives usually loose their edge or just one part of the edge due to just using on narrow stock. Really how often is a hobby shop going to have to have knives sharpened. I can get about 17-20 good sized kitchens made from rough stock out of a set of knives before they go out, this would be years for some. If your dulling fast then something is not right. Your either making to shallow of passes. or have poor quality knives cut at the wrong angle assuming your not using pallet wood.

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Your either making to shallow of passes.

 

Passes can be too shallow?  I've often wondered that when some people will say almost gushing with pride about how they diligently only take 1/64 passes or even smaller to compensate for their underpowered tools.  I'm guessing it causes excessive wear right at the cutting edge where it's weakest?

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I've yet to dull them, but i would like to be prepared to sharpen them when the time comes.  I have a DW734, which has 'disposable' blades.  However, i find it to be extremely wasteful to throw something away when it can be repaired/sharpened with a bit of time and effort.  I just can't buy into the whole 'disposable america' trend we have going on and would like to do my part in overcoming it.  I was just hoping to hear how others have solved the problem of sharpening their blades so that i don't repeat anyone's mistakes.

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Passes can be too shallow?  I've often wondered that when some people will say almost gushing with pride about how they diligently only take 1/64 passes or even smaller to compensate for their underpowered tools.  I'm guessing it causes excessive wear right at the cutting edge where it's weakest?

 

Heat

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I've yet to dull them, but i would like to be prepared to sharpen them when the time comes.  I have a DW734, which has 'disposable' blades.  However, i find it to be extremely wasteful to throw something away when it can be repaired/sharpened with a bit of time and effort.  I just can't buy into the whole 'disposable america' trend we have going on and would like to do my part in overcoming it.  I was just hoping to hear how others have solved the problem of sharpening their blades so that i don't repeat anyone's mistakes.

 

Unfortunately there is a reason they are disposable and its not to just sell you new blades. Are the blades laminated? Are they water jet blades? What angle are they cut at? Are they indexed blade? If so are the index points adjustable?

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the 734 has indexed blades, little pins on the head stick through holes in the blades  they are HSS sharpened at 45*.  I have thought about sharpening mine also.  I guess in theory you could sharpen them down till the point that they no longer protrude, and thus stop cutting.  I would bet we could sharpen them 2-3 times before that would happen.  I haven't tried, though I have been saving them to maybe make them into marking knives, or maybe something useful.  But its pretty low on my to do list.

 

PB, any idea what thickness we "should" be taking off in one pass on a lunchbox planer?

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the 734 has indexed blades, little pins on the head stick through holes in the blades  they are HSS sharpened at 45*.  I have thought about sharpening mine also.  I guess in theory you could sharpen them down till the point that they no longer protrude, and thus stop cutting.  I would bet we could sharpen them 2-3 times before that would happen.  I haven't tried, though I have been saving them to maybe make them into marking knives, or maybe something useful.  But its pretty low on my to do list.

 

PB, any idea what thickness we "should" be taking off in one pass on a lunchbox planer?

 

Don't know never done the math. All knife type planers have a single knife finish cutter head. A non adjustable indexed head allows the factory to keep the finish as good as possible while optimizing feed rate. Meaning the factory has done the adjustment for you to get the best finish with a single knife finish cutter head. When you start playing with sharpening these knives your messing up the cut quality and feed rate. There is no possible way you are not going to change the cutter height slightly. It only takes a very small fraction of an inch to get things off. If you think about it this way. A jointed head can run at 3 times the feed rate of a non jointed head and the difference between the two is very small to small to measure. No sense in making things worse than they already are.

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If the blades are already dull then it seems like a worthwhile effort to me.  Failure would simply result in disposing of them as they were intended.  If it succeeds then you save the money of buying new and save from creating needless waste.  

 

PB, while i appreciate receiving a few reasons as to why it may not have a successful outcome, I think it is folly to suggest so strongly to just throw them in the trash rather than make an attempt.

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PB, while i appreciate receiving a few reasons as to why it may not have a successful outcome, I think it is folly to suggest so strongly to just throw them in the trash rather than make an attempt.

 

If the knives were not indexed I would agree with you. Your just going to add more load to the motor. There is a difference between sharpening a dull knife and honing for maintenance. Honing a indexed cutter is done on the back of the knife not the edge.

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Sharpening/honing jointer/planer knives is not the same as sharpening/honing hand tools… Cutterheads rotate at around 4000RPM, so small things can make a big difference…  I’ll add one or two points for consideration… I use an insert system, so I haven’t tried to sharpen a knife in over a decade, but the info is still applicable…

 

It’s one thing to hone; it’s another to remove metal while refining the bevel. The cutterhead needs to be balanced… If you remove disproportionate amounts of metal from each knife, you may end-up with sharp knives that seem to perform well, but place excessive strain on the cutterblock, bearings, frame, etc…

 

Cutterblocks are designed to a specific geometry for a bunch of reasons that I won’t bore you with… One of the design parameters is protrusion… To maintain effective cutting angle and relief, protrusion must fall within a fairly narrow range. The amount and acceptable tolerance range is different on surface planers and thickness planers for reasons that are out of scope. The correct knife protrusion and acceptable tolerance will be found in the owner’s manual…  By removing metal during sharpening, you may need to adjust the cutterblock’s knife height setting to maintain protrusion within acceptable limits… If not, over time the cutting arc will fall outside of effective cutting angle/relief and performance will fall off…

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==>^^^

 

I'll add one further point: unless you’re meticulous when sharpening your jointer/planer knives, it’s best to send them to a service… A set of knives must end-up with each knife at the same weight and, depending on the cutterhead design, maybe the same height as well… My previous post outlined two reasons why you can carefully sharpen a set of knives, yet the actual performance of the tool drops-off… It’s also the reason to find a good sharpening service – one of the things a service is ‘supposed to do’ is remove equal amounts of metal from all the knives so they end-up with at the same height and weight… The knives are supposed to be checked for uniformity prior to return… If they don’t do this, find another service… I would always recommend double-checking the set upon return from a service…

 

One other point -- unless you use a top-shelf service, you can get a much better edge by sharpening yourself... A top-shelf service will use a multi-grit station so the knives are polished with successive grits (like a plane iron or chisel), say 1K, 3K, 6K, 8K*. However, many services only have a single-grit station, so the knives are polished with a single medium-fine grit, usually 6K. You can check this with a 10x loop… If you get the knife set back and still see a fine scratch-pattern on the bevel, then it’s time to find another service…

 

BTW: when selecting a service, call and ask them exactly how they sharpen the different items -- ask about multiple grits, multi-head surface grinders, etc... If you don’t like the answer, go to someone else... Decent surface grinders start around $250K and the multi-station units are double that... The high-end units are double again… As you might imagine, not every service is going to spring for that level of kit...

 

 

*Note: the numbers given are illustrative, the actual grit numbers are different…

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You have 1/10 of a gram to play with. Any more you running the head to far out of balance. .001 height difference any more the cutter is out of balance. Large industrial machine can run a little past these tolerances little ones can't. Even the huge ones need to be less than .001 height difference to increase feed rate.

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Protrusion is around +- 10thou to maintain geometry. The individual heights need to be within a thou, maybe less. The weight is also a tight tolerance, but I think the tolerance depends on cutterhead length/diameter… Once (and never since), I did find-out the hard way just how important weight can become at 4K RPM… While not obvious, Tersa inserts have different bevel angles depending on metallurgy – many (myself included) mix blade types to get superior results... It’s all kosher because Tersa monoblocks support a balanced pattern… It’s all great as long as you load inserts in the right pattern… Once (and only once) I got distracted and swapped two knife positions… I hit the switch to set the gibbs --- it was impressive to see a 1700lb surface planer vibrate from two items weighing about an ounce placed in the wrong position… It was about time to swap the bearings anyway… :)

 

Now, I use sharpie markers to color the edges on the inserts when I first open the package… I use red, green and blue… Prior to hitting the switch, I just spin the head by hand and watch the colors…

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