Clearance question

Community Discussion šŸ“„ General
1

I have some plywood (18.5 mm). I want to route a groove in it so that I can slip another piece of plywood (18.5 mm) into it. One would think that this would be a rather simple, straight forward deal. Alas, it ainā€™t so :frowning:

How much oversized should the groove be to get a slip fit (not too tight and not too loose) (or what am I doing wrong?)

The cut groove edges are a bit ā€˜fuzzyā€™ so a quick trim with an exacto knife is in order. I would think that having the slot oversized by 0.2 mm on each side should produce the desired results (that generally works for my 3D printer). I am at 0.3 mm on each side (total 0.6 mm oversized) and there still isnā€™t enough clearance. I suspect 0.8 mm oversized should do it but I am concerned that I am doing something wrong with that much clearance required.

When I cut the groove I do not use ā€˜stock to leaveā€™ with a final trim to the exact size. In this particular case I use a 1/8ā€ endmill with depth of cut being 3 mm and a step-over of maximum 2 mm. Is this cut too aggressive and I am seeing cutter flex? How important is it to use ā€˜stock to leaveā€™ when cutting wood (I can see that to be important when cutting metal).

A little guidance from somebody more experienced than me would be appreciated.

2

@Jens one of the problems you might have is that the piece of plywood you are inserting in the groove is not flat, so itā€™s binding against the sides. A small chamfer on both side of the groove could also help inserting the other piece.

1 Like
3

@Jens I know that you use Fusion, Jens. Is that what you are using for this project? The reason that I ask is that, in VCarve, with a stepover that large, it will not allow fine adjustments. The solution is to set a small stepover for the mill in the tool database.
As Iā€™ve said before, I have no clue how it works in Fusion. :grinning_face:

4

The plywood ā€˜appearsā€™ to be flat and I couldnā€™t even get start the insertion with a tilted edge so flatness is not the issue in this case. A small chamfer would help in the insertion but I needed a BFH to seat the plywood in the groove and that would not leave enough room for a bit of glue. I resorted to the table saw to expand the slot a tad so I got the immediate problem solved but I need to learn for the future.

5

Yes, I use Fusion for this project.

1 Like
6

Just to rule out your CAM have you put a pair of calipers on the geometry you cut? 18.5 + .6 should be 19.1 mm grooves. Also like the others said plywood can vary along its length. I would take a few more measurements of the thickness to rule out material variability.

7

@Jens Come to think of it, Iā€™d put the chamfer on the piece you are trying to insert.

8

Make sure you accurately measure the thickness of the wood you are going to insert into the slot.

Plywood thickness rarely measures the same as what is printed on the label.

9

I did what I should have done from the beginning and ran a whole bunch of tests.

As it turned out, the plywood thickness was 18.8 rather than 18.5 mm and the best fit was at 19.3 mm or 0.5 mm oversized.

There was no significant difference between 2 mm stepover or 1.2 (default) stepover. There was a minor difference between cutting right to the edge or leaving 0.5 mm and shaving that off with a contour pass.

My initial run that showed 0.6 mm total clearance would have been ok had I taken a bit more care when measuring the plywood :frowning: