Floor medallion

[cwarner]

At a friends camp for the weekend.  He has a round medallion approx 36" in diameter that he wants to inlay into his solid walnut floor. The floor is pre finished and has been down for 2 years.  The medallion came with a form which is used as a pattern to to router out the floor boards. He said the pattern fits pretty tight to the medallion. He was asking about wood movement which has been his hold up to installing.   I should also mention the medallion is solid walnut and maple.

I have zero experience here but thought to leave 1/16" around the perimeter and caulk but wanted to check here.  The challenge would then be evenly expanding the form for routing.  Anyone with experience here have some thoughts/advice?

[MsNomer]

How thick is the inlay?

[cwarner]

The medallion is a full 3/4" thick to match the hardwood floors

[Bill Holt]

I made two 18" maple & walnut medallions for a customer who installed them tight and then finished at the same time with the floor.  That was several years ago and have not heard of any problems.  IMHO as long as the medallion and the floor are of similar material (solid wood), movement should be similar in both.

In your case, installing in a prefinished floor, I would not be as worried about movement as much as getting them at the same height.  On the other hand, a black caulk ring around the medallion might act as a "high-lighter".

[jasfrank]

I assume the template relies on a standard bushing in the router? You could machine a bushing with a 1/16" larger diameter, or just wrap and glue metal shimstock around the original bushing till it was the correct diameter to give you the relief you desired..

[cwarner]

Thinking about it, he could get one of those multi- bearing rabbeting bits, and set it up for a 1/8" rabbet, and use that around his pattern to expand the pattern 2/3 of the thickness, then use his pattern bit to bring the other 1/3 flush and then he should have a pattern that will leave a 1/8" gap all around the inlay, which he could caulk  and have peace of mind.

[handi]

I have done a lot of inlays in all sorts of materials and thicknesses. 
On the CNC, I always offset to make the pocket 0.007" oversized and the inlay 0.007" undersized. This 0.014" difference is critical to getting a good fit. Without the offset, the parts simply won't fit.

I also tend to cut the pocket with a slight bevel so the top is wider than the bottom. The inlay is cut with a complementary bevel. This creates a scarf joint rather than a straight joint. This hides a world of sins in the fitting. It also allows for wedging the inlay like a cork to force a better fit.

For the size your friend is working in, a 3 degree door bevel Bit would work awesome.