Bit Deflection Help

[Bredmond]

Hey all,

New to CNC here, but I have been lurking for months now.

I'm having an issue with bit deflection and could use some guidance in what to look at to help identify the specific issue.

Bear in mind that I am noticing this now, after having a cut go awry last night and bog down the router and blow the power fuse.

I am cutting 3/4 MDF with a homemade laminate formica top. I am using a .25 downcut spiral (but this was happening on an uncut also).

I have attached a screen capture of my tool settings.

I have also attached a picture of the cutting diagram.

Here is what I was seeing:
-- When the router was plunging to start the cut the whole arm holding the router was flexing up, so that the router was tilting until it forced itself into the cut. I am assuming that this is due to the formica being hard to start the cut?

-- In doing my cuts I saw that my passes were off as they proceeded down in depth. For example:
-- On the long center piece, the right side of the piece was (which is the top right edge on the diagram) it was cut about 1/4 inch shorter on the top 2 passes that it was at the through cuts. On the left edge of the same piece it was cut longer on the 3rd and 4th passes.
-- On the two circle on the right side of the drawing, they experienced a similar problem, however the offset was different, too long on the bottom arc of the top circle (smaller on the same side) and too long on the top of the bottom circle. It didn't appear that the offset matched on those two circles.


My biggest concern is that when I had my issue last night I bent/broke/got something out of alignment and I'm not sure what I should be checking.

Any help would be much appreciated.

Thanks,
Bill

[Danwood]

In my experience If all the machine parts are secured with nothing loose, bit deflection is generally caused by a feed rate that is too high for the bits ability to remove material. when milling metal the feed rates for cutting are well established.
Wood is another matter. Even in the same board I have encountered different cutting characteristics because of knots, Grain density and grain direction.
Because when working in wood there are so many variables it really becomes a problem solved by experimenting with feed rates and depth of cut.
Another factor can be the cutter configuration.
I was making a deep cut in black walnut using a four flute spiral end mill. I noticed smoke coming from the cut. Then I noticed a smoldering fire in the shavings.
I shut the machine off and dealt with the fire.
I did two things.
First I changed to a two flute spiral end mill. ( more chip carrying capacity)
Second I made shallower cuts.
Remember wood ignites at 450 Deg F. It is not that difficult to reach that temperature when making a deep cut and the chips are not cleared from the cutter.
Dan

[basecircle]

Hi Bill let me give this a shot.First thing I want you to check if you have loosened the set scrs.on xand yand z.If these are tight let's start on the programs.First you are cutting some circles with indents in right? You are using a profile cut correct? So cut your pass depth in half.06 and your feed rate to 80.Then go down to tabs .click on it and add a couple of tabs.(so when the cut is complete the part won't jump out.or go into the cutter)Next thing I would do is what is called RAMPing You need this to let the cutter feed into the material There are self explaining on how .Once you add this you will see a big change in the machining.You are correct laminate is hard.but you can feed your cutter nice and smooth and get a good part.I am sure others will chime in.This is a great forum.Also your sizes will hold .So it looks like you were whaleing on the parts.This is a start so I hope I answered your questions. Basecircle

[dcsten48]

Z axis can be out of wack mine is and then don't tell me how to fix

[Adwalker]

Is the dust shoe on the machine? I have experience the dust shoe "whisks" are to stiff when plunging into stock. It will deflect the router off perpendicular.

[gordread]

Bill, I think that Basecircle nailed it. If you do all of what he says you shouldn't have any more problems. If you do, come on back.

Gordon