Mystery Panel Fit

[Birdhunter]

I was putting together two of four 3/4” white oak panel sections using 8mm Dominos. I’ve jointed many panels using the Dominos for alignment. The reference surfaces have always ended up flush to the couch.

These were off just enough to be visible. I measured both side’s mortises and they seemed ok except the wide (I use narrow to wide mortises) mortises seemed a little loose.

I did the other two using a 6mm bit. Those two joined up perfect.

I have plugged up the mortises on the bad two panel sections and will try again later with the 6mm bit.

I measured all the boards and they are all within a few thousands of being 3/4”. They were jointed using the alternate slide to the fence method.

I’m totally mystified! Any ideas.

 

[squall_line]

Is your 8mm bit chipped or worn?

Which part of the joint is off?  The end or the face?  If it's the face, did the fence drift on you?

 

[Birdhunter]

I’ll look at it. Good guess! However, the tenons were a tight fit in the narrow mortise. It was the medium mortise that seemed a bit loose.

I did the first two panels over again with the 6mm and the two pieces went together perfectly. Next is to join the two halves. I learned a longtime ago to minimize glue ups into multiple steps. Eliminates a lot of panic. I also don’t glue the tenons, just the board surfaces. Makes backing out of. A glue up a ton easier.

I’m getting damn good at patching bad mortises. Way too much practice.

 

[Bob D.]

Is it possible that whatever oscillates the bit in the Domino tool has worn over time and when making the wider mortise this wear is more pronounced than with the narrow mortise.

I have no idea how many hours you have on your Domino just asking if this is a possibility. The Domino is only running for a few minutes or less at a time but over years of use I wonder if there is a part or two that wears and causes this condition.

 

[Sparktrician]

[member=15289]Birdhunter[/member], How did you have the panels placed on the workbench when you were making the mortises?  Is is possible that the edge of one panel may have been over the side of the workbench while the side of another may not have been over the side?  If the material is 3/4" thick (19.1mm), it could throw off proper centering of the mortise if the material is not over the side or placed on, say, a small piece of 1/4" plywood to raise the panel enough off the workbench to achieve centering.  Remember that the DF 500 bit is 10mm up over any surface that the machine sits on, so if you're working with 3/4" material right on the workbench and not boosted by some shim material, the bit of the DF 500 may be a touch high, causing the mis-match.

 

[Birdhunter]

I’ve made the mistake of grounding the base and that doesn’t seem to be the problem. I looked at the 8mm bit and it looks ok. Next step is to compare it against a totally new 8mm bit.

All the joints done with the 6mm bit have been perfect.

 

[Birdhunter]

New 8mm is shinier and that’s all I see.

 

[squall_line]

There are so many things that it could be...

Just so we're all on the same page, your /reference face/ is what's not flat?  And only this one time with the 8mm bit/tenon?

If your typical usage is the 6mm, are you applying pressure the same with the 8mm as you do with the 6mm?  Plunging slower with the 8mm than the 6mm to account for the increased resistance of the larger bit?

Any chance the piece or the machine moved on you?

Have you tried again on some scrap with tight-loose?

Have you tried on scrap with loose-loose and tight-tight, to verify it's cutting the same on each piece of wood when the width setting doesn't change?

Obviously the loose setting should only change the width of the mortise from side to side, not the thickness, but I wonder if there's a small offset happening because of a stuck something or other.

 

[rvieceli]

[member=15289]Birdhunter[/member] have you tried repeating the joinery on som scrap with the 8 mm bit? Just to if wasn’t some sort of weird anomaly?

Ron

 

[Birdhunter]

I’ll do a repeat on the same white oak using an 8mm bit.