Holdfast Rotary Vacuum Adapter

[Edward Weingarden]

I Just received the Holdfast Rotary Vacuum Adapter for my Grizzly G0800 lathe. The quick disconnect on my vacuum hose does not stay on the male end coming off the vacuum adapter. Does anyone know how to make the connection between the vacuum adapter and the vacuum hose? Thanks.

[Brice Rogers]

When I look at the picture of the holdfast, the "nipple" looks like it is for a push-on tube and isn't a quick disconnect. Is this the situation?




My vacuum setup just uses push on (semi-rigid) poly tubing. Everything stays in place

[Walter Mooney]

I have to agree with Brice. That end is what I think is called a barbed fitting, so the tubing just pushes onto that fitting.

[Eugene Dixon]

Try a small wire tie. If that does not work, try wrapping a piece of wire around it and twisting it tight. Be careful of loose, pointy ends.

[Edward Weingarden]

Brice's picture is what I have. The 3/8" ID hose I use for my vacuum system will slide on to the nipple. I'll try putting a cable tie around the hose end on the nipple.

Brice - is your push on poly tubing connected in some way to a quick disconnect? Is your poly tubing a direct connect to the Holdfast System? I use a Gast vacuum pump. Thus, the set-up with compressor hose and quick disconnects.

[Brice Rogers]

I'm using a Thomas pump (very similar to the Gast) and I have (IIRC) 3/8" threaded fittings that screw into the pump but the other end of the first fitting is a barbed fitting. I slide the semi-rigid poly tubing over the barb and they fit tight enough that I don't need or use clamps. I think that for the vacuum gauge and the bleed valve that I had to use a 3/8 pipe-to-barb fitting.

I have my vacuum bearing mounted in a disk of wood with a dovetail that my regular chuck grabs. The other side of the wood disk has the craft foam on it. the vacuum bearing has a fitting glued into it to which a 1-1/2" long nipple of poly is permanently attached. The I.D. is perfect in that my poly tube slips inside of it with a decent vacuum fit. So when I remove the vacuum chuck, I just slide the smaller tube out of the slightly larger tube. Same at the other end. So my poly tubing acts as my "quick disconnect" of sorts.

All of this is from Bob Leonard's frugalvacuumchuck design. Check out his website for ideas and to get a visualization of what I described. Even with two slip fits (with the poly) and the barbs w/o clamps, I can easily get 25 inches of vacuum (and I'm at about 2,000 feet so that will cut out roughly a couple of inches).

[John K Jordan]

..... I can easily get 25 inches of vacuum (and I'm at about 2,000 feet so that will cut out roughly a couple of inches).

Curious as how you figured that. 2000 ft is about 600 meters.

The Engineering Toolbox (very handy web site, btw: https://www.engineeringtoolbox.com/a...ure-d_462.html) gives

• 29.9" at 0 meters (sea level)
• 28.9" at 1000 meters (about 3300 ft)
• 27.8" at 2000 meters (about 6500 ft)

Do you mean you're at 2000 meters instead of 2000 ft? Or maybe I don't understand atmospheric pressure and vacuum.

I've heard nothing but good things about the frugal vacuum, talked to him at symposiums. If I were buying today I think I'd get things there. https://www.frugalvacuumchuck.com/home.html

JKJ

[Edward Weingarden]

I'm using a Thomas pump (very similar to the Gast) and I have (IIRC) 3/8" threaded fittings that screw into the pump but the other end of the first fitting is a barbed fitting. I slide the semi-rigid poly tubing over the barb and they fit tight enough that I don't need or use clamps. I think that for the vacuum gauge and the bleed valve that I had to use a 3/8 pipe-to-barb fitting.

I have my vacuum bearing mounted in a disk of wood with a dovetail that my regular chuck grabs. The other side of the wood disk has the craft foam on it. the vacuum bearing has a fitting glued into it to which a 1-1/2" long nipple of poly is permanently attached. The I.D. is perfect in that my poly tube slips inside of it with a decent vacuum fit. So when I remove the vacuum chuck, I just slide the smaller tube out of the slightly larger tube. Same at the other end. So my poly tubing acts as my "quick disconnect" of sorts.

All of this is from Bob Leonard's frugalvacuumchuck design. Check out his website for ideas and to get a visualization of what I described. Even with two slip fits (with the poly) and the barbs w/o clamps, I can easily get 25 inches of vacuum (and I'm at about 2,000 feet so that will cut out roughly a couple of inches).

Thanks Brice

[Brice Rogers]

John,

I've been using a rule-of-thumb for a while and you made me recheck it. I thought perhaps that I was wrong and had been for several years. So, I did a quick google search and came up with this: https://anver.com/vacuum-lifters/atmospheric-pressure/

Altitude Above Sea Level (feet)	Altitude Above Sea Level (meters)	Atmospheric Pressure (psi)	Maximum Vacuum Level Attainable (inches Hg)	Vacuum Level Loss at Altitude	Maximum Vacuum Level Possible at this Altitude
0	0	14.70	29.921	–	–
1000	305	14.16	28.9	3.4%	96.6%
2000	610	13.66	27.8	7.1%	92.9%
3000	914	13.16	26.8	10.4%	89.6%
4000	1219	12.68	25.8	13.8%	86.2%
5000	1524	12.22	24.9	16.8%	83.2%

So, I thought that I should double check that with another un-associated site. I also looked at another "hit" on the google search that gave this rule-of-thumb: "As a general “Rule of Thumb”, for every 1000 feet above sea level, the maximumpossible vacuum is reduced by approximately one in-Hg (0.491 psi). By using this ruleone can quickly determine the maximum possible vacuum for the area. " (reference: https://vacmaster.zendesk.com/hc/en-...um_Systems.pdf)

I don't understand why the Engineer toolbox site would differ so much. It does seem to be a feet-to-meters error somewhere.

BTW, I really like the bearings that I get from the frugalvacuumchuck guy. I learned the hard way that many so-called sealed bearings are "non-contact" seals. That is, for a vacuum chuck they leak pretty badly. Bob's bearings are good. I can turn off my pump and my part will stay in place for perhaps 30 seconds.

[John K Jordan]

John,

I've been using a rule-of-thumb for a while and you made me recheck it. I thought perhaps that I was wrong and had been for several years. So, I did a quick google search and came up with this: https://anver.com/vacuum-lifters/atmospheric-pressure/
...

Thanks for that! Gives me a reason to do some more looking. Maybe even drag out some old textbooks. [Gasp!]

JKJ

[Glenn C Roberts]

The table below indicates air pressure at elevations below and above sea level.

Altitude Above Sea Level		Absolute Barometer		Absolute Atmospheric Pressure
feet	metre	inches Hg	mm Hg	psia	kg/cm2	kPa
-5000	-1524	35.7	908	17.5	1.23	121
-4500 aprox. deepest point under sea level of Sognefjorden, Norway	-1372	35.1	892	17.2	1.21	119
-4000	-1219	34.5	876	16.9	1.19	117
-3500	-1067	33.9	861	16.6	1.17	115
-3000	-914	33.3	846	16.4	1.15	113
-2500	-762	32.7	831	16.1	1.13	111
-2000	-610	32.1	816	15.8	1.11	109
-1500 shore of the Dead Sea, Palestine, Israel and Jordan (-1371 ft)	-457	31.6	802	15.5	1.09	107
-1000	-305	31.0	788	15.2	1.07	105
-500	-152	30.5	774	15.0	1.05	103
01)	0	29.9	760	14.7	1.03	101
500 aprox. Møllehøj, Denmark	152	29.4	746	14.4	1.01	99.5
1000	305	28.9	733	14.2	0.997	97.7
1500	457	28.3	720	13.9	0.979	96.0
2000	610	27.8	707	13.7	0.961	94.2
2500	762	27.3	694	13.4	0.943	92.5
3000	914	26.8	681	13.2	0.926	90.8

https://www.engineeringtoolbox.com/a...ure-d_462.html The first column is feet.

[John K Jordan]

Well I finally took a closer look and I believe your table is correct. All I can imagine is a probable brain burp, er senior moment! The same table I used earlier doesn't say what I thought it did yesterday morning. I found other tables and a couple of pressure/altitude calculators. (Anything to avoid doing the math!)

My only defense is I'd been operating power equipment early and suddenly started to feel dizzy so I turned everything off and came up to the house to rest a bit. At least I was thinking clearly enough to quit! Thanks for the correction!

PS, how did you copy that section of the table from the web page into your message? It looks great. I've tried to do that before without typing in a bunch of code but did succeed.

JKJ

[Glenn C Roberts]

John, all I did was highlight, copy & paste. Not sure why it works most times and not others.