Losing my mind? Domino indexing off?

[bruegf]

I think I'm losing my mind. 

I've adjusted the index pin and when I make the first mortise on each of the two mating pieces using the tightest fit and check,  the edges of the two pieces line up perfectly.  After I make the rest of the mortises (loose or tight) and check the fit again the the edges have a very slight offset.

I swear the darn thing is messing with mind.....  Its done this on a number of different pieces even though it doesn't seem possible.

Any ideas what might be going on here?

Thanks

Fred

 

[Michael Kellough]

Are you using the pins to make a series of mortices in the same board? It's a little unclear what the problem is.

 

[bruegf]

Sorry, yes, I'm using the index pins to make a series of mortices across the edge of a board.  I've done this just using the pins in the base of the Domino and also using the cross stop pins. 

I think I've discovered the problem.  It seems that by the time I've done a number of mortices enough error has accumulated that the center to center distances between the outer mortises on the mating pieces are very slightly different (approx 1/64 over 16").  They are close enough that the pieces will join, but just enough different that it pulls one piece ever so slightly away from the outside edge.  If I only insert a domino in the mortise closest to the edge I index from the edges of both pieces are flush.  If I  also insert a domino in the mortise furthest away from the first one the edges of the pieces are longer flush.

Fred

Fred

 

[Michael Kellough]

Sorry, yes, I'm using the index pins to make a series of mortices across the edge of a board....It seems that by the time I've done a number of mortices enough error has accumulated that the center to center distances between the outer mortises on the mating pieces are very slightly different (approx 1/64 over 16"). 

And that is why they gave us the option to use wider mortices. It should be possible to get the pins adjusted perfectly but even if you acheived that there is the problem of debris in the mortice, inconsistent pressure on the pin etc. making your spacing inconsistent so it's usually best to use use penciled registration marks and a wider mortice setting for subsequent mortices in a row.

 

[Jerry Work]

Hi Fred,

It is not a good idea to try to make a whole series of tight mortises sequentially.  It is too easy to not  register the pins in the center of the previously cut mortise and, as you point out, the cumulative very small error can bite.  Best technique is to make one or two tight mortises then shift to a wide mortise, then back to the tight for a couple.  That way the intermediate loose mortise will provide the necessary variance for any pilot error without changing the strength of the assembly.  M&T joints derive most of their strength from the faces of the tenon to mortise fit, not the edge fit.

Jerry

Sorry, yes, I'm using the index pins to make a series of mortices across the edge of a board.  I've done this just using the pins in the base of the Domino and also using the cross stop pins.   

I think I've discovered the problem.  It seems that by the time I've done a number of mortices enough error has accumulated that the center to center distances between the outer mortises on the mating pieces are very slightly different (approx 1/64 over 16").  They are close enough that the pieces will join, but just enough different that it pulls one piece ever so slightly away from the outside edge.   If I only insert a domino in the mortise closest to the edge I index from the edges of both pieces are flush.  If I  also insert a domino in the mortise furthest away from the first one the edges of the pieces are longer flush.

Fred

Fred

 

[bruegf]

I ended up going back and cutting wider mortises to correct the problem.  I used the tight mortises on the panel lay up I did as the first use of the domino and all 30 mortises in the 6 piece lay up fit nearly perfectly so I thought it would always fit as well.  Probably the difference between cutting the mortises on teak as opposed to melamine covered particle board.

Thanks for the feedback everyone

Fred