Home-Made Box Joint Jig

[j]

Hi,
I've been lurking here for a couple of weeks, now I think it's time to get some advice.

I've made a basic box joint jig for my very basic router table. I've run one sample on a couple of scap bits of wood and it fits togeter surprisingly well. However, If I hold it up to the light, I can see some gaps between the fingers. These are very small, probably <1mm I'll try and measure it with my calipers, but I think it's just too small to measure. maybe i'll see how many sheets of paper I can fit in there.

I'm a bit unsure as to what part of the jig is out of alignment, or what I can do to be more accurate. The joint is quite tight to put together, any tighter and I might break something if I force it.

Would glue help close the gap at all?
Any other advice on fine tuning it?

Thanks.

 

[MikeW]

Hi j, welcome!

Depending on how much and where the gaps are (all against one side of the fingers or random) glue can take care of a lot.

Too, if one creates too tight of fingers the joint can actually become glue-starved. imo it is better to have some small amount of space. It's the amount that is the issue.

One way to tell if the jig is cutting off, is, can you put it together with just hand pressure? If so, then the small amount you are experiencing may be due to a little movement min the jig as it pass across the bit, the router's run-out (where the bit is actually moving side-to-side, no matter how little it compunds on each cut).

If there is not an even amount of gap or if it progressively gets larger, it can be the jig is ever so slightly off in spacing between the cutter and whatever you are using to index the position.

Also, when holding the wood, pressure one way or another against the wood towards or away from the index itself will move the wood ever so little.

I would take two pieces and make a test joint and glue them to see how it really fits.

Mike

 

[devonwoody]

Hello lurker, clever getting away with just a "j" for your username.

If your finger joint has been constructed from softwood it most probably is down to the timber quality or condition. Chipboard and MDF have their problems to.

Otherwise I would have thought that the template system you are using to space joints is most probably the other cause or movement as you pass the timber across the cutter.

 

[Waka]

J

Welcome to the forum, do you have any pic's to show us?