RoarRocket Hand Pump Veneer Press ?

[Ken Massingale]

Keith and anyone with one of these....

I just picked one of these up at WC.
Have you tried laying a vacuum guage in the bag to read the vacuum? I tried an auto test guage that I know works and can't get any deflection of the needle. But, the bag is definitely being evacuated, it gets very tight to the netting and stock, and I can see the veneer flattening to the substrate. I've only done dry runs so far.
Thoughts?

[WayneJ]

You need to put the hose in the bag, not the whole guage. Its outside air pressure that makes the guage read. Its the difference between the inside and outside pressure pushing on a diaphram that makes the guage move. I have a vacuum pump that I made from an old refrigerator compressor that I used for a/c work. It will pull 28in of vacuum, should work well Just need to find a way to hook it to a vacuum bag.
Wayne

[drumpriest]

Since you asked me by name, I feel that I should be helpful, but I don't know that I can be, sorry. I havn't tried a vacuum gauge with the press. I can only speak to the results I have seen while using it. It certainly does evac the air and get tight around my cauls.

[Ken Massingale]

Thanks Wayne and Keith.
Wayne, what you say makes sense now that I think about it. I was basing putting a guage in the bag on a pic on Joe Woodworker
Check the pic near the lower right.


Does the guage being liquid filled make a difference?

Thanks again
ken

[LCHIEN]

Thanks Wayne and Keith.
Wayne, what you say makes sense now that I think about it. I was basing putting a guage in the bag on a pic on Joe Woodworker
Check the pic near the lower right.


Does the guage being liquid filled make a difference?

Thanks again
ken

The fluid is for damping- vibration and shock protection and should not affect the reading.

This kind of gauge is a bourdon tube based device. A curved tube where pressure inside wants to make it straighten out and rotate the dial.

There are two kinds of pressure readings - PSIA and PSIG.
Both require pressure differences on the tube.
The PSIA (Absolute) measures pressure relative to a sealed pressure (vacuum or one standard atmosphere) while the PSIG (Gauge) has this reference open to the atmosphere which is local atmospheric pressure.

One therefore tells you the absolute pressure and the other the difference between local atmosphere and the inlet.

If you seal an absolute pressure gauge in a vessel and evacuate it it will still read the vacuum correctly which is what the guy in the link must have had.

If you seal a guage pressure device in a vessel then it will indicate zero pressure or vacuum since the reference is also evacuated. This is what you had.

Normally, on a device in the open at near sea level in normal weather the two types of gauges will give nearly the same reading (too small a difference to tell). But change the atmosphereic reference...
and there will be a world of difference.

Interestingly enough, you can convert a PSIA guage to a PSIG gauge by drilling a hole inthe reference chamber and opening it to the local atmosphere. (but it's inside so its not that easy to do...)

Often but not always the gauge is marked with PSIG or PSIA.

A differential pressure gauge actually has two ports, one for the normal inlet and the second port for the reference pressure. (PSID, I think)

[Ken Massingale]

Thanks Loring. Excellent explanation and I think I understand now.
ken

[BigguyZ]

Ken- I just got one of these kits at my local Rockler for $30 and was wondering why you are testing it. Is it to make sure you're getting decent results? Has that been an issue before with these kits?

[drumpriest]

Sounds to me like he was curious. I've gotten good results using this kit. It does take practice to get the correct amount of glue on the surfaces. Too much and you can get glue pockets, too little and you can get bubbles where it didn't adhere.

The second you can fix with a pin vise, some glue, and a clamp. The first is irreparable.

[BigguyZ]

Sounds to me like he was curious. I've gotten good results using this kit. It does take practice to get the correct amount of glue on the surfaces. Too much and you can get glue pockets, too little and you can get bubbles where it didn't adhere.

The second you can fix with a pin vise, some glue, and a clamp. The first is irreparable.

What type of glue do you use? The guy at Rockler said he uses Tightbond yellow glue...

[Ken Massingale]

Ken- I just got one of these kits at my local Rockler for $30 and was wondering why you are testing it. Is it to make sure you're getting decent results? Has that been an issue before with these kits?

Just getting familiar with it before actually doing some veneering. Also, I would like to know the vacuum in the bag, but that's just me being curious.
Have you checked the woodworker section at the Roarockit site? They have a few good tutorials and tips, including glues.
$30??? Real good price.
ken

[drumpriest]

You can use regular wood glue, but there is a titebond for veneering called "cold press". It is less likely to saturate your veneer and keep finished from taking. Many veneers are 1/32 to 1/48 of an inch, so this is a concern. If you are cutting your own veneers and doing 3/32 like David Marks, this is less of a concern, which is probably why he uses regular wood glue or plastic resin depending upon the project.

[kwgeorge]

I am a user of the Titebond Cold Press and I like it a lot. I have used it on all the veneer projects I have posted here and have exceptionally good luck using it.

Ken

[drumpriest]

Yeah, I don't think that I made it clear in my previous posting, but I use the cold press and have had good success with it as well.