View Full Version : Need Help! Surfacing

05-17-2014, 03:35 PM
I have my machine working very well for someone of my experience. I did a test cut after making some changes in Drivers and changing from Uni-polar to Bi-Polar wiring. I cut 3 squares and 3 circles 2" , 3" and 4" they came out very well almost dead on.Now I need to check my Z-axis for accuracy. I think I am good for movement up and down. My problem is I tried to cut a pocket with a 1.5" bottom cleaning bit. I had a set of squares with little hills and valleys. Not flat at all. is this the bit or is my Z-axis not parallel.I cannot not afford a surfacing spoil board bit. These are $200 to $400 for a bit I would only use very little.

Thank You


05-17-2014, 06:39 PM
Just get a nice large straight cutting bit, like this one that I use - Grizzly.com (http://www.grizzly.com/products/Bottom-Cleaning-Bit-1-2-Shank-1-1-2-Dia-/C1261)

Works wonderful to surface the MDF spoilboard. You just have to do more passes then with a real spoilboard/planing bit.

edit, and I completly misread the post. sorry about that.

Yes the hills and valleys means your z-axis and spindle are not perpendicular to the table.

05-17-2014, 07:19 PM
The hills and valleys are signs that you need to tram your spindle. If it's anything except perfectly vertical, then it'll leave an irregular surface, as you describe. The way to measure it is to attach a dial indicator to an arm that's perpendicular to the axis of rotation. I use a block of wood that has a 1/4" hole drilled in it, and another at right angles, sized for the shaft the indicator mounts to. I sawed the block down the middle, and when I put a 1/4" pin in the collet of the spindle, I clamp the block around both shafts. Now, with the indicator touching the surface, I can swing the whole thing around, measuring the distance in +X and -X , and +Y and -Y. The goal is to tilt the spindle such that everywhere around the circle measures the same. That means the axis of rotation is perfectly vertical.

You'll need to actually cut a surface large enough to measure in that way. It can be a piece of MDF clamped to your table, but it needs to be flat, overall, to your linear rails. Just measuring to the spoilboard before cutting won't be as accurate as measuring an already cut piece, since the spoilboard is only approximately flat to the rails, as built. Try to position the indicator in the same "terrain feature" wherever you take a measurement. ie: always in a valley, or always on a hill, so the surface irregularity is accounted for.

If I recall correctly, the CNCRouterParts mount is set by loosening the bolts and just tilting for the Y axis, and shimming behind it for X. (shim at the top of the mount to tilt back, and at the bottom to tilt forward, obviously. If you don't have an indicator, they're not terribly expensive, and they're a really great thing to have around. I got the cheapest set from LittleMachineShop Dial Indicator, Magnetic Base & Point Set - LittleMachineShop.com (http://www.littlemachineshop.com/products/product_view.php?ProductID=1782) and it's fine for this application.


05-18-2014, 01:14 PM
This is the bit (http://www.amazon.com/Roman-Carbide-DC1261-2-Inch-Cleaning/dp/B005W18EIW/ref=sr_1_3?ie=UTF8&qid=1400432313&sr=8-3&keywords=DC1261) I am using. I may need to try a smaller cross over.

Trotline I am going to check out the alignment. I have a dial indicator. I guess I am confused on how I am getting perfect squares. I am going to try step over first as nlancaster suggests.

05-18-2014, 01:35 PM
Look at me assuming - presuming and and not checking. It is the router bit. It is not flat. I thought that as a bottom cleaning bit it would be flat. It is not I just check with a straight edge.it is shaped like and upside down v very shallow but it is cupped.

nlancaster you say the Grizzly one is flat. I will get that one. I only need to flatten small pieces no larger then maybe 18x18.


05-18-2014, 01:39 PM
some marks will remain even most careful indicating..

for the bit... just use whatever on hand.. takes more time, but don't have to buy at this moment.. if a part smaller than 2x2 inch, then you use anyway jig or other aux stuff.. like a vise.. and those will lay flat..

05-18-2014, 02:08 PM
I thought that as a bottom cleaning bit it would be flat. It is not I just check with a straight edge.it is shaped like and upside down v very shallow but it is cupped.

It' s like that so the center doesn't rub and burn the material. It will cut flat. If there are ridges or steps between passes, then your spindle isn't perpendicular to the table.

05-18-2014, 03:34 PM
Right, the bit is spinning very fast. As Gerry said it is normal for there to be some relief in the center of a flat cutting bit.

05-18-2014, 05:02 PM
OK then it is back to what Trotline has stated. Check my Z for parallel. Thank you everyone.