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Double Cut Saw, thickness problem on ends

PostPosted: Thu Mar 12, 2015 10:55 am
by travishclm
We are having a problem with some sniping on the ends of our boards. Not every board but a high percentage. Board is correct thickness after the complete saw enters the cut. Sawing only on the front cut or only on the back cut the problem boards are only 30 to 40 thousandths off. But when sawing both directions it can be off as much as 60 to 100 thousandths. When measuring one to two ft off of the end of the board it is back on target thickness. We are a hardwood mill and the problem is the worst when sawing denser woods. White oak shows the greatest variance. Can't get my head around this sniping issue, any help would be greatly appreciated.

Re: Double Cut Saw, thickness problem on ends

PostPosted: Mon Apr 06, 2015 10:42 am
by thinkerf
My first thought is about the lead of the saw. Double-cuts are generally set up parallel to the carriage rails.

Second though is how fast are you entering the cut. If you enter slowly, does the problem go away?

Bruce

Re: Double Cut Saw, thickness problem on ends

PostPosted: Mon Apr 06, 2015 11:39 am
by rich
You might check guides to make sure you are not inadvertently leading the saw with miss aligned guide or miss machined guide.

Re: Double Cut Saw, thickness problem on ends

PostPosted: Mon Apr 06, 2015 12:08 pm
by Mensawjohn
I would agree to check the guide alignment. If they are correct it could be a strain problem. Is the saw dodging knots?

Re: Double Cut Saw, thickness problem on ends

PostPosted: Mon Apr 06, 2015 1:08 pm
by myquest
We had a similar problem and it was related to stress relieving the log. The opening cut was made and, depending on the length of the log and where the dogs held it we would see thin ends and thick middles or some combination of it. The sawyer would open up a log and the log would bow out due to relieving the stress, his return cut would result in thin ends if it was a ten foot log with the distance between the knees being seven feet. I tested this theory with nails and a string and using a square and a set of digital calipers. Some logs would bow out as much as 0.100" after just one cut. When the log was turned over the stress would equalize resulting in a perfectly square cant. I have that spreadsheet somewhere, that was many years ago. Good luck. Of course this is after alignment issues have been checked and resolved.
Good luck and stay sharp.
Mike

Re: Double Cut Saw, thickness problem on ends

PostPosted: Mon Apr 06, 2015 1:55 pm
by wbsaws
Yes, first thought was guide alignment. Put a magnetic base dial indicator on a part of the carriage and measure the face of some freshly installed guides top and bottom.
Many areas in the sharpening can be considered. Make sure the grinding wheel is over the centre and square of the saw blade. Side clearance and clearance angles are the same on both sides.
Best of luck.
Tony