Newbee unable to machine a flat top

[jdonaldson]

I'm trying to machine a flat top on my sacrifical board but I get scalloping on the two sides the top and bottom are flat. I thought that maybe I didn't have the router seated correctly but have reseated it and still get the same results. I've attached pictures of what it looks like and would appreciate your help

Thanks

John

[jdonaldson]

opps forgot the attachment, it's two big will have to resize and send

[cdat]

What kind of bit you using?

[Consultingwoodworker]

I used to install and service industrial woodworking CNCs. (still do occasionally) Part of that process is "tramming" the head, which is insuring that the spindle is exactly perpendicular to the bed. The lines you see are from the disk of the bit cutting edge being at an angle to the bed.

You can check this by running the head up, and chuck a 1/4" steel rod into the collet. The longer the rod, the more accurate the check. Use a square to check the rod against the base checking left, right, front and back.

But what I see in the photos is that the ridges tend to follow the cut line. If your head were out of alignment, the ridges would all be in the same orientation. What bit, feed and depth were you cutting at? If you were cutting too aggressively, the bridge can flex, which would cause the issue I see in the photos.

I flatten my MDF bed with a 1/2" dia bit set to cut 0.010"

Ralph

[jdonaldson]

Thanks for all the input, I think from all the input that i was trying to hog to much, first try was with 3/4" bit set to .125 don't remember the feed rate, 2nd try was with same bit set to .05. will try this evening with 1/2" bet set to .015

Thanks for all your help

John

[RhB_HJ]

I used to install and service industrial woodworking CNCs. (still do occasionally) Part of that process is "tramming" the head, which is insuring that the spindle is exactly perpendicular to the bed. The lines you see are from the disk of the bit cutting edge being at an angle to the bed.

You can check this by running the head up, and chuck a 1/4" steel rod into the collet. The longer the rod, the more accurate the check. Use a square to check the rod against the base checking left, right, front and back.
..............

The other method to check if the spindle and/or Z- axis is perpendicular is use a test indicator with an extension arm to swing out a 360º circle.

[Consultingwoodworker]

HD,

I actually built a custom indicator like that with a 24" swing. Super accurate. I just figured that the average user would not have one.

Maybe I should post plans for making one from a drill press circle cutter.

Ralph

[RhB_HJ]

Ralph,

Good idea!

And when the admin and moderators get around to it, they could transfer/duplicate some of the many suggestions over to the Setting up the Shark section. That would make a good start on getting a bit more order i.e. things would be easier to find (without using the "Search" function).

[jdonaldson]

HD,

I tried resurfacing using a 1/2 bit at .015 still ended up with the scalloping on the two sides so i'm thinking that the router is fairley square from front to back but off left to right, would like to see what your custom tool to check this looks like and also how do you adjust the router.

Thanks

John

[Consultingwoodworker]

Start with a circle cutter, the kind with the adjustable arm. Replace the pilot drill with a 1/4" steel pin. (this is to fit the 1/4" collet.)

Mount a dial indicator onto the end of the bar. That will allow you to take readings at opposite points. The longer the bar, the more accurate the reading.

Hope this helps,

Ralph