RAS miter problems

[Eric Mims]

Hi, I am trying to make a 45 miter with my radial arm saw. I have
'tuned' the saw as best as my sanity will allow, using 2 RAS books and going through all steps multiple times.

The blade is a brand new Chopmaster 10" with stiffener. I made a miter jig that I clamp on. The problem I am having is that it seems to be cutting more away upon entry of the piece (I'm talking hair widths, but enough that matters in a picture frame).

On a 3/4 x 3" of oak, the cut is perfectly smooth but when I hold my straightedge to it, it is straight cut except for the entry area (perhaps an inch length fades from square and I can see slight semi circular saw marks in that first 1" or so when looking at the cut). I have tried clamping the workpiece, I have tried sawing in reverse and when I did that it seemed to have the effect but from the opposite side. I even tried using a backing workpiece thinking maybe the saw was deflecting. This offset my workpiece 3" of course and allowed it to enter the workpiece already under work, and somehow it still had the same effect (so I don't think it's a deflection from the RAS arm or motor housing). I don't understand. :confused:

[glenn bradley]

Since you used a sacrificial piece to get past the offending entry area and still see a problem I would double check the gauge you are using to check the cut with.

[Loren Hedahl]

I would venture a guess that what could be happening is the torque of the motor is being resolved in the first part of the cut as the blade enters the wood. One way to control this is to make a rough cut out about 1/16th of an inch. Then make a final skim cut to the correct dimension.

Another possibility is the piece being cut is slipping slightly on the jig. This can be controlled by gluing sandpaper to the jig's fence. A grit of about 100 will work OK. You could even clamp the workpiece to the fence. Using a stop at the other end also prevents this kind of creepage.

Good luck, and I think you are on the right track to use a jig instead of swinging the arm.

Loren

[Eric Mims]

Thanks for the ideas. I checked it along the whole length and both sides of my Starrett 12" square as well as my imported machinist squares. They all show the uneven line.

I have tried clamping the piece and holding it very securely but it seems to show the same tendency. I thought having the backing piece would eliminate the problem but somehow it didn't. Could it be the actual blade or heel/toe of the blade?

As a side note, I went to a local store to buy a Lion Miter Trimmer today (they had one that had been sitting forever for a good price), and I hadn't placed it on hold because I knew it had been there forever..well guess what? It was sold between when I called the other day and today! I was so bummed.

[Ray Klear]

Try putting a peice of scrap in front of the peice your going to cut. The blade will resolve itself in the scrap and the peice you use should have a good cut
just my 2

[Rick Christopherson]

I'm thinking that you might have some blade runout. If the inboard arbor flange is removable, try removing it and putting your blade stiffener on the inboard side. I actually have two blade stiffeners on my 12" RAS because the stamped steel flanges are not flat, so I removed them.

The blade could be wobbling as it first enters the cut and then settles in to the kerf.

[Al Killian]

The motor assembly could need to be tightened up. If it is lose it would lead to it twisting when you first start.