Moulding crush in Underpinner

[pixnut83]

L&G,
I have been test driving my 'new-to-me' Pro-Turner underpinner and getting towards passable results.
Flat-topped sections are fine, but domed profiles, particularly those of lower density material, are badly crushed where the top pad impinges on the moulding. I've tried reducing contact pressure using wadding but that makes little difference. Should the pad be close to the moulding, 1/2", 1"...prior to pressing the pedal? The pad is pulled down by springs so I guess the larger the initial gap the less the spring is extended and hence there is less clamping force - but how do you assess it so that you exceed the upwards force as the V-nail is driven in? Is it trial and error or experience, or is there a more deterministic solution?
I suspect I may have answered my own question, but any advice, hints & tips would be welcome!
I'm rapidly running out of scrap section to experiment on!
Thanks,
John.

[Roboframer]

I've no experience of that machine.

My pneumatic one has three different pads - a rock hard one and two (one shorter than the other) with rubber pads that take the form of the moulding on contact - plus the air pressure can be reduced for fragile mouldings.

But when I had a manual underpinner- the pressure pad was on a threaded rod - is yours?

I'd start with the pad raised too high on the thread - press the pedal until the pad was as far down as it could be without the hammer engaging - so that the 'first pressure' was taken - then, holding the pedal in that position, screw the pad down on to the moulding so it was just about touching. That was it 'set'

For hardwoods you could screw down a couple of turns after that and for more delicate ones you would want to screw back a turn or two.

Lion do a gizmo that may help


...................................

[prospero]

I use an ancient manual Euro. The pressure pad is covered with thin felt and it basically, next to useless. Years ago I made a little wood triangle and covered it on one side with 1/8" cork sheet. This spreads the load. No denting. Only prob is that the cork gets gunged up with hardened lumps of glue, which will make marks, but I got round this by wrapping the triangle with handywrap which can be replaced easily.

I have a number of improvised add-on pads to allow correct pinning of awkward-shaped moulding. Sometimes on reversed moulding, a chrevron of the same moulding mitred backwards is very handy.

[Nigel Nobody]

Wet suit material (neoprene) makes great padding for use with a vee nailer block. 10mm thick for softer woods.
Excess glue washes off easily if you do it immediately after using it.
For some of my long gone vee nailers, I made a right angle triangular block with the side that make the right angle three inches long, from 16mm MDF or plywood and glued the neoprene on the bottom of it.

[JFeig]

In addition to the hardness/softness of the hold down foot there is or might be an air pressure question. I as well, do not know the machine you have; but, my machine has multiple valves to control the separate air pistons (driver piston, hold down piston, inside the corner hold piston.

I have also custom designed extra hold down feet. They were made from hard rubber hockey pucks and contoured in several designs .... large triangle, dog leg, and dog leg with an inside bevel. The shaft that is inserted into the base of the air piston is from a properly sized bolt to fit. My OEM foot was also modified with a crape rubber cushion (from a rubber cement takeup square) vs thick felt.

[pixnut83]

Thank you for the hints and suggestions. I'll make a bigger pad with some compliance out of MDF and neoprene.
The Pro Turner is foot-operated (non-pneumatic); the single action pedal starts by pulling the top pad down to contact the moulding. Pressure is maintained by springs (and the force increases) while to pedal is further depressed to activate the hammer.
I think my pedal action of one continuous stroke is at fault; this causes the top pad to impact the moulding - almost like hitting it with a hammer. I now reckon this is the main cause of the damage. What I should do is depress the pedal lightly until the pad contacts the moulding and then push with more firmness to activate the nailer.
Hopefully, modifying my foot action in conjunction with a spreader pad should improve matters.
John.

[Judders]

I've no experience of that machine.

Hi Roboframer,

This answer you gave re. the probs incurred when using an old Turner Underpinnner interested me, as I occasionally have a tendancy to damage the curved soft gold and silver mouldings, the same as pixnut had in these columns way back. You suggested the Lion gizmo might help, see attached from catalogue, but this is for the Casssese underpinner and I should like to know if you think it would fit the Turner.

My pneumatic one has three different pads - a rock hard one and two (one shorter than the other) with rubber pads that take the form of the moulding on contact - plus the air pressure can be reduced for fragile mouldings.

But when I had a manual underpinner- the pressure pad was on a threaded rod - is yours?

I'd start with the pad raised too high on the thread - press the pedal until the pad was as far down as it could be without the hammer engaging - so that the 'first pressure' was taken - then, holding the pedal in that position, screw the pad down on to the moulding so it was just about touching. That was it 'set'

For hardwoods you could screw down a couple of turns after that and for more delicate ones you would want to screw back a turn or two.

Lion do a gizmo that may help

[Roboframer]

These are my pressure pads, no idea if they'd fit the Turner underpinner, but if not maybe they could be adapted.

pressure pads.jpg

pressure pads 001.jpg

[Not your average framer]

I use the Lion adjustable magnetic head on my CS-88, I still have the set of Cassesse pads, but I have not needed to use them since buying the adjustable magnetic pad.

While we are talking about underpinners, many underpinners can be adapted and improved when the need arises. I also have a Gielli 4000e which is an air powered machine and I am looking into the possibility of fitting the Minigraph sprung claw rebate clamp onto the Gielli. Most of these things are not rocket science, they just need a little figuring out.

In general manual underpinners have two different springs for the top clamp and the wedge driver. The weaker spring allows the top clamp to operate first and when the top clamp engages the moulding then any further movement of the pedal begins to move the wedge driver.

When the wedge driver has reached the limit of it's available travel, any further travel on the pedal will tend to compress the pressure pad material and as the this material becomes compressed there may be a point where the moulding starts to be compressed instead of the pad.

In all likelyhood the pressure pad is not spreading the pressure over a large enough area and may also benefit from a softer and perhaps thicker pressure pad material.

Just a thought, but if the adjustable magnetic pad will fit both the Cassesse and certain Pro-Turner underpinners, the perhaps the Cassesse pressure pads will also fit the Pro-Turner. I would ask a few questions first, before jumping in the deep end and buying any Cassesse pressure pads, just in case this proves to be wrong.

I hope some of this helps,
Mark

[Jonny2morsos]

I bought one of the Lion pressure pads and although not using it much initially I now find it is used for 90% of the mouldings I join.

The ability to slide it in and out to contact the most appropriate part of the moulding profile is, I think, its major plus point. iIt also spreads the pressure over a wider area than the Casesse pads.

[pixnut83]

L&G,
The ProTurner - more correctly, its operator - is now getting good results. I made a triangular load-spreader which is a 4" square of 1/2" plywood, cut diagonally and faced with self-adhesive foam rubber. Along with a few L-shaped bits of MDF for spacing to get the load-spreader horizontal I now get reliably good, uncrushed corners. The pressure post needs to be set appropriately as well so the pre-load onto the top of the moulding is 'just' sufficient to exceed the insertion force of the V-nail.
I average only around 5 to 10 frames a week, so I can take my time to experiment.
But most of my work now is plainwood with flat top, Ash, Oak and Obeche mainly, finished as required with stain, wax, liming wax.

The Morso is behaving beautifully, by the way.

How big is the Lion magnetic head? (along the legs of the contact pad)
John.