Lee Harps

I was asked by fellow harpmaker, Al Winter, of Silvershell Musical Instruments, to join him in presenting a program about using vacuum to accomplish veneering and as very effective clamping device. We had presented it some time ago to our local woodworkers’ club, SAW-PA, and were asked to repeat it for the York club, the Susquehanna Trail Woodworkers’ Guild. As a hobbyist woodworker, I must admit that I personally felt a little intimidated by the task ahead, knowing that many of the York club are quite skilled craftsmen. I’ve learned that, at my age, one just barges ahead and hopes for the best. I couldn’t have been more pleased with the reception we received and the interest shown by the group!

The setting was just wonderful! The York group meets on Princess St. in York in the lobby of the Industrial Museum. Here is a photo of president, Ray Parson, leading the preliminary club business meeting.

It was a wonderful space for the meeting and the attendance was quite good. Early on, I noticed a man taking lots of photos. I learned, as the evening progressed, that his name is Bob Aspey and it just so happens that their club has an official photographer and HE IS THAT MAN! At the end of the evening, he offered to send me some photos by email and, with some arm twisting, he generously agreed to mail a CD of ALL his photos to me. A few days later, the CD arrived with 62 photos on it! Bob further gave me permission to use them here, so the remaining photos in this entry are thanks to you, Bob! I hope you don’t mind if I did a little cropping along the way to make the photos best fit my narrative.

Vacuum clamping is probably one of the most effective methods available for applying even, intense pressure over a given clamping area. Both Al and I have “gerry-rigged”, home-built suction devices that we took along. This was mostly a show-and-tell event, with Al and I sharing some of the devices and procedures we use in our own shops.

Here are photos of our vacuum pump setups, first mine:

and then here’s Al Winter with his ELEGANT vacuum pump (he takes great pride in telling how, at a yard sale, he only paid $5.00 for the little pump on the bottom — clearly worth many many times more than that !)

Here are Al and I about to get started with the demo – here, Al’s “spiffy” vacuum unit has not yet been lifted to the table. You can see some of the props we brought along for the demo.

To demonstrate the primary reason I have developed a vacuum veneering setup for my workshop, I brought along the harp I have built of eucalyptus wood which has a rounded back, formed with the vacuum bag technic.

In the “rough”, here is how the rounded back looks “right out of the bag”, so to speak, the “bag” being the vacuum bag!

What you see here is a fiberglass-covered foam form over which is formed a combination of two inner layers of 1/8 inch bending plywood and an outer layer of veneer of choice; in this instance the veneer is of PURPLEHEART wood, a somewhat rarely used wood from South America.

Here I am holding a photo which shows the various ‘layers’ that are necessary to perform a vacuum-veneered round-backed harp shell.

Before I permitted Al to have the floor, I described the components of a veneering operation and actually did a small demo veneer glue-up to show the group. It would be drying throughout the remainder of the demonstration. First, I showed them the components needed: a substrate, pieces of veneer, glue, waxed paper, a caul to make the surface flat, a piece of wire screen to permit distribution of the vacuum, a vinyl vacuum bag, a bag closure device and the vacuum pump connected to the bag with the white hose.

The blue tape in the photo above is used, in addition to veneer tape on the underside of the veneer, to keep the veneer pieces tightly together until the veneer is glued in place.

Here I am applying veneer glue to the substrate (plywood) over which the veneer will be applied.

A wooden layer (caul) is placed over the veneer to provide equal distribution of the pressure over the entire surface, thus assuring a very flat finished product. Since veneer glue is “squished” out from the pressure, a sheet of waxed paper is applied immediately over the veneer to prevent the caul from being glued to the finished product.

Here, the glue has been applied, all the layers are in their proper places, so the entire “stack” is then positioned inside the vinyl bag in anticipation of the application of the vacuum.

Using a special wooden closure device and Quik-Grip clamps, the vinyl bag is sealed, the vacuum pump is turned on, and the air has been evacuated from the interior of the bag. The vacuum applies, at 20 inches of mercury, about 1200 pounds of pressure per square foot, evenly distributed across the surface of the item being veneered.

At this point, I turned the program over to Al. Al described in some detail the components necessary to make a functional vacuum setup, including the valves, reservoir tanks, gauges, tubings, vacuum switches and, of course, the CHEAP VACUUM PUMP!

Another function that a vacuum pump is excellent for is that of holding one’s workpiece for other functions such as routing, sanding, etc. Some wood turners, I understand, are also using vacuum to chuck their wood to the lathe for turning.

Here Al is showing a vacuum system that does not use a CHEAP PUMP, but rather attaches to one’s air compresser and uses the Venturi (fly sprayer) principle to create a vacuum. This is probably one of the most inexpensive approaches to vacuum veneering, provided one already owns an air compressor. Here is a closeup of the Venturi device.

Al also described how one constructs the vinyl bags, the special vinyl glues one uses and the precautions one must take in doing so in an effort to prevent liver damage from breathing the fumes. He showed how leaks may be sealed in the bags by applying liquid vinyl glue to the leaking areas while under vacuum so that the vacuum will draw the glue into the leaks, thus creating a seal. A very complete resource for all supplies needed (and pages of very valuable advice) can be found online at Joe Woodworker, a supplier who is in the Baltimore area if I’m not mistaken.

Al then gave a very neat demo on the use of vacuum as general workshop clamping device. Here he has constructed a special vacuum jig which he uses in forming his harp necks. The plywood center has foam window stripping both on the perimeter of the under surface and, on the top, in the shape of the harp neck.

By applying vacuum to either of the brass fittings to the right of the photo, the board is “sucked” firmly to the table top and the harp neck is firmly drawn down to the top surface, all at the same time! When one side is completed (sanded, routed or whatever), he releases the vacuum, reattaches the vacuum tube to the opposite side, flips the harp neck over, and once again, draws the workpiece tight for finishing on the other side. This is very efficient and such a reliable and rigid clamping device!

Al also demonstrated a handled device he has made which, unlike the neck device which attaches itself to the table, holds the workpiece in a more portable manner, this way giving the workpiece a temporary handle for machining or shaping. Here he is with the workpiece firmly “vacuumed” to the handle:

Do you think it’s very tight? (Sorry, Al, I had to include this photo!)

There was considerable interest in the harp I had brought along, so I spent some time describing the challenges of building a harp that is both structurally sound enough to withstand the constant 1200-plus pound tension of the strings, yet to make it light and delicate enough to have a decent tone.

I described how the two narrow glue joints, one at each side of the soundboard, must be durable enough to remain intact with the string tension tugging at the center of the soundboard 24/7!

At this point, an hour and a half had passed very quickly and it was time to remove the sample veneer project from the vacuum press.

The blue tape had to be removed. In some cases, the tape, even though it is supposed to be a low-tack tape which comes off easily, took some wood fibers with it on removal. A man who was present who does veneering for a living told me afterwards that his shop never uses tape on the surface for that reason. Here is the finished product:

Both Al and I were most gratified by the way we were received by the Susquehanna Trail folks and received a great deal of enjoyment in doing our presentation. We learned much ourselves from those present. Thanks for the invitation and, once again, thanks Bob for the use of your photos.

Another regular feature for woodworker events is that the membership do a bit of show-and-tell. Here is an item that was brought in by Dean:

This is quite a work of art. Dean is a master wood turner (meaning he works on wood that is spinning around on a lathe). This piece began as a most interesting piece of 3/4 inch wood with a very unusual and unique burl pattern. Somehow, Dean managed to turn a 1/4 inch circle on each side of the wood, leaving the remaining center section 1/4 inch thick as well. He is most adept at doing lathe projects that seem impossible and we always look forward to see what he has along for each meeting. Thanks Dean for sharing your talents with us!

This entry was posted on Sunday, September 3rd, 2006 at 10:15 pm and is filed under Doin's In the Workshop, Things "Harpy", Uncategorized. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.