John
I have read in some books that after installing newly sharpened jointer blades it is a good idea to joint them with a stone that you rest on the out feed table. As I recall they suggest that the back of the stone be wrapped in paper to protect the out feed table. Can you comment if this is necessary or advisable. If it is a good thing to do is it something that could be done periodically to ensure the blades remain sharp?
Bob Vergette
Pender Woodrat
Replies
Scary...
Bob,
Jointing the blades as you describe, is mentioned occasionally in old books, but I have never done it myself, and see no reason to try. The practice is obviously dangerous, can damage the machine, and I doubt if it would improve the finish of the cut enough to compensate for the risks involved. I seem to recall that there was a posting here in Knots years several ago from someone who tried it and they shattered the stone.
If I were going to try it I would use a fine grinding compound rubbed into a hardwood block instead of a stone, at least you wouldn't have to deal with flying stone chips, but I still wouldn't do it myself.
Jointer knives
Hi John,
I noticed that you have a fair amount of experise with jointers so the question comes to you. Recently, I posted a question on replacement blades for a 15" jointer and I would appreciate if you could shed some light on the subject of the type of steel is best and any direction to a reputable manufacturer of knives in general. Thanks
Bob,
Old timers used to use this practice to extend the life of dull knives, not new ones. The idea was that you could "dress" dulled edges by honing them in the cutterhead once or twice before sending them out to be sharpened.
It is a risky practice, and, along with the use of "built-up" shaper cutters, tilting table tablesaws, and unguarded bandsaw wheels, pretty much a thing of the past, like all those 4 fingered woodworkers who made use of them. Gaw, I miss those days.
Ray
ray, so, does gumming a
ray,
so, does the thought of gumming a circular saw blade make ya hanker for the by-gone times as well?
eef
eef,
My dad had a "gumming
eef,
My dad had a "gumming wheel" for his grinder, and yes, I remember when circular sawblades were steel, hand filed, and gummed; and carbide tipped blades were a new and wondrous thing.
Heck, I've even been known to file, gum and set a two-man crosscut. (Boy, I don't mind you ridin' your end of that thing, but do you have to DRAG YOUR FEET??)
Good ole days were only good compared to now.
Ray
Jointing Knives
Like most woodworking kills, jointing knives in a cutterhead can be pretty "scary" if the operator has no knowledge of what he is doing or why he is doing it....
The process of jointing has little to do with sharpening the knives, which when installed are hopefully sharp to begin with.
With the best of effort and jigs, when installing multiple knives in a cutter head the result will be a one knife finish as one knife will be higher than the others. Finish quality is dependent on knife marks per inch, the more cuts per inch the better the finish, up to a point*, and knife marks per inch is determined by multiplying the number of knives finishing by the RPM of the cutter head divided by the feed speed in inches. Therefore for a three knife cutter head at 3600 rpm with a board being passed over it at, say, 40 feet a minute there will be 7.5 knife marks per inch. If, however, all three knives are finishing then there will be 22.5 knife marks per inch.
The process of jointing the knives will bring them all into the exact same cutting circle which will increase the finish quality for a given feed speed.
The jointing procedure creates a "land" on each of the knives and although it looks like a secondary bevel, it is not, as the surface of this land is in contact with the work piece. Once the land gets too wide the knives will hammer the wood and degrade the finish,(not to mention the noise will scare off all the neighborhood cats).
I have not gone into the procedure itself as Ferier does an excellent job of it in his book, Cabinetmaking and Millwork, available used from Amazon or a library. I have found those "old guys" in many cases actually knew a thing or two.
In summary:
1. Jointing will bring all knives into the same cutting circle, thus allowing for a smoother cut and superior finish for a given feed speed.
2. It can be used to refresh a dull edge or remove minor nicks, within reason. Remember, once the land gets too wide, the finish will degrade. It will become quite obvious when this becomes the case.
3. Prior to jointing, the knives should be carefully installed, within a few thousands of each other- as all knives will be jointed to the low knife, sloppy setup will result in an unacceptably large land.
4.When done properly and with a backstop for insurance is perfectly safe, as the stone is lightly sparking off the knives.
5.A hard stone is required, the stone should cut the knives, not the other way around. Molder supply companies can supply the proper stones for low RPM applications.
* Past a certain point, say approaching 30 KMPI, the chip load will be unable carry away the heat resulting in premature dulling of the tool and degradation of the finish. A good example of this in the extreme is the burning caused when a board sticks in a planer.
Excellent Information
Rob's response contains enough sound technical knowledge to remind me of that old Fine Woodworking Magazine that was around about 20-25 years ago. Everything he says is sound and accurate, and of value to the serious woodworker, even though one can spend a lifetime and never need to joint knives in such a fashion.
The info regarding 'one knife finish' is important to know and is a fact that refutes a lot of techno-babble from equipment and tooling vendors.
I can add that some of the better machines - Northfield in particular- offered a small grinder that mounted to the outfeed table in order to powerjoint the knives quickly and safely.
I will also second the remark about the noise level. I have a certain range of hearing totally absent in my right ear from the old 18" Northfield Patternmaker's jointer with jointed knives screaming while I flattened thousands of feet of Hard Maple.
Dave S
Acorn Woodworks
Another way to skin a cat (instead of scaring them off)
I read (and used) a technique to sharpen the jointer knives in place with the machine un-plugged.
In this method the outfeed table was lowered to allow a paper covered stone to not just joint the knives but to sharpen them without the lands and heat issue. To hold the knives the author drilled a small hole in the infeed table to hold an indexing tab. I was horrified at the thought of drilling into the machined surface so I made a flexible stick that I clamped to the infeed table instead. In practice the technique worked for a number of resharpenings before the knives needed to be sent out for grinding. It made all the knives exactly the same height to the outfeed table (a big bonus if you do not have magnetic knife holders) and was simple. The only fussy part of the process was to keep the machine clean (and bearings) while sharpening and resetting the outfeed table to the correct height after the process was complete. I used this technique a long time ago but now with magnetic knife holders and money to spend on regrinding, I have abandoned it.
Robert.
Another easy option
I just buy two or three sets of premium blades - at least T-1 steel, swap them whenever they become dull, and have them professionally sharpened. I hate working with dull or knicked blades. Whenever it's time to swap I put on some nice music and get a sandwhich and lawnchair and take my time with it. I use every alignment tool at my disposal, place every blade perfectly and double check it, and when one invariably slips out of place during the tightening sequence I loosen things back up and fix it. I know the job's done when the outfeed table is leveled and none of the blades protrude more than say .001" to .002" more than the rest (checking both the front and back edges). Back in the day I used to try honing the edges by hand to make them last longer in between changes, but honestly by the time the cutting edge is gone they were usually a little knicked up anyway. To me the jointer is one of the most important machines in the shop. It creates the reference face for everything I do.
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