underpinner forcing join apart with scoop profiles

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andj

CGF, Certified Grumble Framer
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Sep 30, 2006
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I am trying to join a frame with a scoop profile but my underpinner is creating a gap when I drive the nail in. I have a mitre-mite vn42 and I am joining larson juhl profile 320940. Anyone know how to drive the nail without separating the join? Thanks!
 
I have the same problem with some profiles. I just don't use the front pressure clap. I have the 4L but I do think the clamping system is about the same.

It could be because your mitre cut are not 45 degrees. I would check my cuts to be sure that they are perfect.
 
Have you tried using a triangle block to spread the pressure over the face of the moulding. I cut a 90 degree shaped (triangle) piece of 9mm MDF which I place over the corner in the clamps, so when the bung comes down it distributes the downwards force over a larger area than the face on the bung
 
Keep the downward clamp close to the top of the moulding and make sure the vnails are aligned with it. If the vnails are being shot in to far ahead or behind the hold down clamp it causes the moulding to rock or separate. Also use appropriate vnails for the type of wood you're joining.
 
I had a couple of mitred dowel rods of different diameters. I would put the correct one in the scoop, then put a triangle piece of plexiglas on top of the whole thing, which made it all approximately level. Then shoot as usual, because the pressure will be equal (or close) over the whole face of the moulding. Hope this helps....
 
On some of those scoop profiles I find it easier to glue and clamp and nail the joint.....you know, like in the old days....
 
Very simple profile to join on the VN 42. Mine has the 90 degree hold down clamp which is the best configuration. Use a single 10mm wedge and insert it in the back first. Do not stack. Place one toward the rabbet and let the glue dry. Be sure the hold down clamp rests on the high point of the back edge when inserting.

With the 90 degree hold down clamp the v-nail inserts in the center of the clamp so you only want the back edge of the clamp on the moulding. Stacking v-nails in this moulding will cause a problem.
 
Pictures Please

Could some of you show some pictures of your concoctions. I am having some trouble visualizing some of what you are describing. I don't see an easy way to attach something to the front clamp.
 
That is quite a scoop, I have found that with some profiles I had to cut short pieces of the moulding and then invert them and place on top of the moulding to be pinned, it gives a flat top for the clamp and you can use a little more pressure as it is distributed better.
I also have 1/2" thick felt "L" pads which I can put on scooped moulding to conform to the scoop and protect the moulding.
 
If this VN 42 is configured with the 90 degree hold down clamp it has a teflon pad on it and needs nothing else. It will not mar the finish and only a small amount of the edge of the pad needs to be on the back edge of the moulding. It will hold the scoop portion with no problem as long as the outer v-nail is in place first. Anyone with a VN 42 that does not have the 90 degree hold down needs to get the clamp and throw all of the other junk in the trash.
 
Jeff, the problem I occasionally had with the teflon pad on the 90 degree clamp with extreme scoop profiles was that just the corner of the pad contacted the moulding and would sometimes dent the frame. So I started using the felt pad in those extreme cases.
 
It would have to be a very extreme scoop on a very soft finish. It is best to take the prssure down to 60 lbs in that case. I keep mine around 80 for most items.
 
My problem isn't with the upper hold down clamp, its with the front clamp that put s pressure against the lower rabbit.

With mouldings that have a rounded black, the front clamp will sometimes push the miter apart. Sometimes the upper clamp will push it back in place, sometimes not.

The lower clamp is only 1/8" tall. If it were closer to the height of the rabbit, it wouldn't push rounded mouldings apart as much.
 
Larry do your back fences rock and roll. I have found that tilting the back fences all the way forward stop much of the gapping issues you describe. I have seen the VN 42 set up without the ability to tilt the back fences.
 
Another thing to try is to move your rabbet clamp one hole farther back than you normally would. It will still engage but with less pressure.
 
Larry Peterson said:
With mouldings that have a rounded black, the front clamp will sometimes push the miter apart. Sometimes the upper clamp will push it back in place, sometimes not.
Click to expand...

In some such cases I do a little dance... I omit the front clamp entirely, hold the two legs of the moulding with both hands, and press the plunger with my right forearm. Hokey, but it works!
 
Jeff Rodier said:
Larry do your back fences rock and roll. I have found that tilting the back fences all the way forward stop much of the gapping issues you describe. I have seen the VN 42 set up without the ability to tilt the back fences.
Click to expand...

Mine tilt, but in the wrong direction for this. They tilt out from the bottom. After spending too much time getting the back fences at a perfect 90 degrees and the fences perfectly vertical, I really don't want to mess with them unless necessary.
 
Mine tilt forward and backward using a nob with a center line. I adjust the angle fairly often for different mouldings.
 
jim_p said:
In some such cases I do a little dance... I omit the front clamp entirely, hold the two legs of the moulding with both hands, and press the plunger with my right forearm. Hokey, but it works!
Click to expand...

That's exactly what I do -but on the 4L I have the foot pedal for the top plunger. Don't really need the front clamp on any moulding of you don't mind using a little muscel.
 
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