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?


https://www.woodturnerscatalog.com/images/prod/400/hol_vac_ada-5.jpg

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/air-altitude-pressure-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-us/article_attachments/202402637/Effects_of_Altitude_on_Vacuum_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/air-altitude-pressure-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.