Page 2 of 3 FirstFirst 123 LastLast
Results 16 to 30 of 39

Thread: Jointer Problem: Results in boards concave up along their lengths

  1. #16
    Jacques,I agree that is the best method to adjust out feed table height.But in this case the tables have been adjusted ffor parallel ,and still might not be parallel .

  2. #17
    Join Date
    Aug 2009
    Location
    'over here' - Ireland
    Posts
    1,605
    My sympathies Brett! Per my recent posts it can all get a bit frustrating and mind boggling. Especially (as in my case too) after years of running a machine that just happened to be OK as delivered - that only ever needed the knife heights set.

    There's a lot to be said for stepping back to let the head clear a bit. One issue (you can run into the same one when adjusting motorcycle suspension ) is that unless you are an experienced machine guy and very clear on what adjustment does what (and more to the point what it can and can not compensate for) it's easy to get lost as a result of making very small adjustments so that the change isn't evident in the performance of the machine. Sometimes it's worth taking a fairly large step to find out...

    As the guys have said the good news is probably that since your machine was working acceptably well before adjustment it's likely to only be either table coplanarity or knife height that is the problem - and it sounds like since you adjusted the tables that that may have been the issue.

    I'm still flattening tables on mine and have to put the theory to the final test, but i've concluded that even very minor dips and rises in the tables can especially if in the wrong place require the them to be set slightly out of apparent coplanarity to compensate - so that the actual parts of the surfaces on both tables that the wood rides over are flat/coplanar relative to each other. i.e. coplanarity checked over the full length and width of the tables with a long straight edge and feeler gauges can be misleading if the edge not resting on/passing over exactly the right part of the tables - at least not unless the tables are pretty much absolutely (within a thou or two) flat all over. Likewise if its not perfectly straight.

    Which (in support of the 'who needs to measure to a few thou tendency) tends to suggest that once coplanarity is set in the ball park using a straight edge and the knife heights are about right that it's maybe best to 'dial in' the cut by raising or lowering the outer end of the infeed table (prob best leave the outfeed alone, as this avoids messing with its relationship with the knives/knife height) to get it cutting straight or slightly concave as you require. If by then it looks like the tables are drooping or its about to take flight then maybe look for causes.

    The downside of this approach is that the machine may joint differently depending on where across the width of the table the work is placed - an issue perhaps masked by the fact that many jointer tables are very narrow and hence not much out of flat across the width of the tables. (potentially a much bigger deal on a 12in or 16in machine though)

    Knife height (once all three knives are set the same and parallel to the edge of the outfeed table by your favourite method) as the guys say seems fairly straightforward. Start with the outfeed table a bit high and the work will drag on it - you feel the resistance, and it increases any tendency to cut convex. (which could be masked/reversed/exacerbated by the effects of table coplanarity) Gradually lower the outfeed table (maybe 0.001in or less at a time) and the resistance fades and the cut straightens out a bit. Keep on lowering the outfeed table/raising the knives and eventually it will start to produce obvious snipe at the trailing end of the piece as it drops on to the knife just after it clears the indeed table - depending on the table situation it may by this stage be by now starting to cut a little concave as well.

    Trials so far seem to suggest that knife height doesn't make all that much difference to the straightness of cut however. If the knives are high relative to the outfeed table there probably is the potential to cut an apparently (but not truly) concave edge if weight is transferred to tip the work off resting on the infeed and on to the outfeed table at about half distance - but at the expense of the need for sensitivity as to how the work is handled to get consistent results, and getting snipe at the trailing end.

    My tendency is to suspect (despite the tendency of machine makers to suggest otherwise by listing very wide flatness tolerances for tables, and to describe apparently straightforward adjustment procedures) that in practice there's only a very very narrow range of knife heights over the outfeed that work well, and that after that it's about practical flatness/actual coplanarity of the tables...

    ian
    Last edited by ian maybury; 01-02-2013 at 6:19 AM.

  3. #18
    Ian,I was with you until close to the end where 'knife height doesn't make all that much difference to the straightness of
    the cut'. That is the only routine adjustment, excluding depth of cut by infeed adjustment, and it's the main cause of climbing ,snipe ,and unwanted concave or convex surfaces. An understanding of that adj and how nicks and slight dulling to the knives affect it is primary. I can't reconcile your rejection of that with your determination and credible knowledge on scraping the tables.

  4. #19
    Join Date
    Aug 2009
    Location
    'over here' - Ireland
    Posts
    1,605
    That's OK Mel, you did well to even read that far It's a great help to be able to double check stuff with others. I'm as you know just finding my way on this. Could be that I've been too cautious on my knife height adjustments, or that i'm missing something. I seemed to get instant responses to small changes in table coplanarity, while on the knife height snipe seemed to be setting in before there was much change in the cut...

    ian

  5. #20
    I read them all several times, keep us posted ! Don't recall reading what type and length straightedge you are using...

  6. #21
    Join Date
    Jan 2010
    Location
    Montgomery, Texas
    Posts
    287
    Thanks Ian, your sympathies are much appreciated!

    So, I'm about twelve hours in now and still don't have acceptable results. I feel as though twelve hours is a very generous amount of time considering the setup time indicates one hour in the manual and video. I think as woodworkers we all have a sharp eye to detail and precision and I'm an engineer by day so point being is that I feel that I should be getting very accurate results.

    The problem is that I don't know what to do next. Just to reiterate, I've reset both the infeed and outfeed tables twice now, along with the knives each time. I've watched the videos and I find myself saying "yep, did that" over and over. Insanity is starting to set in and I don't know if trying again for a third time is a losing battle. The factory settings are long gone so what should I do?

    I don't have a high quality straight edge so I could start there. Any recommendations? I noticed Lee Valley has a reasonable anodized aluminum for about half the prices of the steel edge.

    I'll also check on the knives and maybe another sharpening service. I do take my knives and blades to a local supplier and sharpening service where the pros go so I do have confidence in them. Any recommendations on a magnetic knife setup jig? That should help minimize any additional error, even if it's .001". Maybe as an excuse, I looked at the Byrd replacement head and didn't realize the sale was though 12/31 so that's probably out.

    It's too bad none of you are close because an experienced second set of eyes sure would help.

    Thanks and keep the ideas coming.

  7. #22
    I googled making a straight edge ,the one useing three pcs to verify looks good.

  8. #23
    Join Date
    Jan 2004
    Location
    Lewiston, Idaho
    Posts
    23,758
    Brett,

    I have a G0490X. I felt I needed a straight edge to check it's set up. I bought this one from Grizzly http://www.grizzly.com/products/36-B...h-Scale/T21580 . The first straight edge showed up and it had one end that the last 3" weren't withing the 0.001" guaranteed specification. I called Grizzly...no problem....we'll ship another right out and keep the first one.

    The 2nd one was dead on.

    I prefer steel over aluminum because aluminum is softer and more prone to "dinging". As sure as the sun rises in the east, if I bought an aluminum one, I would damage it accidentally. It only takes one moments slight carelessness to make a ding.

    Did you watch the video to which Shiraz linked? Have you checked your jointer using the methods shown in that video?
    Ken

  9. #24
    Join Date
    Aug 2009
    Location
    'over here' - Ireland
    Posts
    1,605
    I have a 24in Woodpecker's guaranteed straight edge Mel - but because it's too short to use to check coplanarity have been using a good quality extruded box section aluminium level a bit longer than the two tables to check that. It too seems to check out as being straight.

    Pardon my coming in again on the main topic Brett/guys, it's to head off (hopefully) any risk of my having caused confusion. I should just say that despite my comment to Mel about not finding that knife height adjustments changed the cut on my machine so much as dropping the end of a table (which latter shouldn't be a required normal running adjustment) that of course the knife heights are a key factor and still need to be set right.

    It's definitely necessary as the guys are saying to check them before anything else if they have been sharpened and re-fitted - but the heights not subsequently checked against the out feed table and each other.

    +1 with Ken and Mr. Grizzly on working through the set up in the Grizzly video too. Since the tables have been disturbed they need checking for coplanarity. Since the machine was previously working well then table flatness should as before NOT be a factor. i.e. set the tables coplanar and get the knife heights 'right' and it should joint straight.

    One standard way to check knife height is the 'carry forward' test recently discussed and also described in my own ???? jointer set up thread - but be careful of the knives and make sure the power is off before rotating the cutter by hand.

    As a starting point they should probably be set to generate around 2 - 3mm of carry forward to within way under 1mm variation (in carry forward) across the width of each knife and from knife to knife at every point checked - which means checking at say the middle and at both ends of each knife and adjusting it's height where needed until the carry forward is within this range. Depending on the blade holder and adjustment method (machines with built in height adjustment in the knife holders may not need anything) you may need something like a magnetic knife holder to hold them in place when doing up the locking screws.

    If its still not cutting quite right then some fine tuning of the knife height may be required as has been described earlier in the thread...

    ian
    Last edited by ian maybury; 01-02-2013 at 10:14 AM. Reason: clarity

  10. #25
    Join Date
    Jan 2010
    Location
    Montgomery, Texas
    Posts
    287
    Ken,
    Yes, I did watch the video that Shiraz shared and as mentioned before, I found myself mentally checking off the boxes of doing all of the steps they went through. Of course, I followed the detailed instructions in the manual as well and in the order suggested--outfeed, infeed, and knives.

    The eccentric bushings are not easily turned as indicated in the video using a punch even after removing and loosening both sets of set screws. I tried a punch initially (as recommended in the instructions too) and found that I was damaging the two grooves on the eccentric bushing with each blow. So, I switched to a wrench but with such a large mouth opening required for the wrench, some spots are very difficult to maneuver the wrench. The instructions did also mention a mechanics wrench (can't recall exactly) but similar to a wrench used on an angle grinder to lock and unlock the blade.

    I did look at that particular straight edge so are you happy with it now? I read a few reviews on other sites that weren't favorable so I wasn't sure of the quality, especially to risk it as my go-to precision straight edge. Also, I wasn't sure if the accuracy of 0.001" was over the entire 36" or over 12" as some are specified, resulting in 0.003" tolerance over 36". How did you measure the inaccuracy in the last 3"--feeler gauge?
    Last edited by Brett Bobo; 01-02-2013 at 10:53 AM.

  11. #26
    Join Date
    Jan 2004
    Location
    Lewiston, Idaho
    Posts
    23,758
    Brett,
    I am happy with the replacement straightedge today. The first one I got did have the last 3" that didn't meet the 0.001" specification. I placed it on a machine surface and it was obvious the last 3" weren't touching..I could see light...I used feeler gauges to measure the error.....carefully marked on the surface.....swapped it end-for-end....180 putting it back within the marks and the error followed the same end. When I got the replacement, I checked the original against the replacement and it showed the same thing....one end of the original straightedge.....3" on one end wasn't straight. Would I buy it again? Yes...it's a good value for the price.

    I would recommend rechecking everything using a straightedge......don't check them off mentally...take time check them as shown in the Grizzly video....don't make any adjustments initially....... This isn't rocket science....the jointer is one of the simplest stationary power tools in our shop but ...it requires that very tight tolerances be maintained between 4 surfaces. Three of these surfaces must be parallel....the 2 beds and the cutterhead....

    Good luck!
    Last edited by Ken Fitzgerald; 01-02-2013 at 4:40 PM.
    Ken

  12. #27
    Join Date
    Mar 2011
    Location
    Houston, TX
    Posts
    72
    Just out of curiosity, how are the knives set in relation to the outfeed table? Sorry if I missed it already listed in the thread. I had this same problem when my outfeed table was too high. It wasn't high enough to stop a board on the outfeed table though. I adjusted the outfeed so that rotating the knives would move the straight edge forward by 1/8". That did the trick.

    One thing that may be worth mentioning, before doing this I also experienced a fair amount of resistance when pushing a wider board through. After the adjustment, boards go through pretty easily. Mine is the G0490X by the way.

  13. #28
    Join Date
    Jan 2010
    Location
    Montgomery, Texas
    Posts
    287
    Dustin,
    The knives are set following that same approach of just "kissing" the bottom of the straight edge as the cutterhead is rotated around. I probably spent a hour alone each time trying to dial in the knife heights to be sure that was correct as well. I've noticed that when tightening the gib bolts, the knives can shift slightly so there's some trial and error to set them correctly. I do still have a concern that the knives may not be perfectly square across the 8" length as previously mentioned. This becomes obvious when the knives don't touch the straight edge exactly the same way, e.g. moving 1/8" forward, at all positions along the length of the knives. Granted, this is being very picky and shouldn't yield the results I'm getting but it is something.

    Since you're in Houston, I take all of my blades and knives to Circle Saw and have had good success with them in the past. In fact, they use a 24" planer knife that they've machine sharpened as their straight edge to setup their equipment so I do feel confident that my 8" knives should be straight.

    I'll take another stab at it and probably post some more photos in the next couple of days on my progress.

  14. #29
    Join Date
    Aug 2009
    Location
    'over here' - Ireland
    Posts
    1,605
    Hi Brett. Sounds like you set the knife heights, but just be aware (as you may already know) that a thou or two in height relative to the out feed table can make quite a difference. The guys have seen it more clearly than I have, but it sounds like it can affect the curvature/straightness of the cut quite bit too.....

    ian

  15. #30
    On planers and jointers I spray oil on the gibs, cutter head,and knives .Adjust gib screws to where knife easily moves.Hold knife with magnets ,tighten .Knife does not move when being tightened . Exact procedure varies with each machine but
    favorite system on jointers are the old ones with knife index wheels and my homemade magnet gauge.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •