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What You Need To Know
About Vacuum Chucking
(A non-technical approach)
by Mickey Goodman mgoodman@tiac.net
Over the last four months I have received an education
on making a vacuum chuck as well as buying a vacuum pump and developing
the hook-up from the pump to the lathe.
I decided I would share my "education" with the rest of the woodturning
folks.
The information I have gathered came from manufactures of vacuum pumps,
websites, people selling vacuum pumps on EBay, other clubs and other
Woodturners.
1. Vacuum Pumps
I spoke to a lead technical person at one of the most recognized vacuum
pump manufactures who told me that for vacuum chucking you need a pump
that would pull at least 25 inches of vacuum and have a CFM of at least
4.5. What does that mean?
Well, the 25 inches of vacuum means how much "sucking" power the pump
has to establish the vacuum. The CFM is cubic feet per minute that the
pump can draw.
Why is that important? If your pump can draw a vacuum to 25 inches,
which is sufficient for a wood turner’s purpose but the CFM is down to 1
or 2 and because of leakage, it can’t maintain the suction to the
level necessary to hold your piece in the vacuum chuck (all the inches
of vacuum doesn’t mean a thing if you can’t maintain the vacuum). This
lesson was learned the hard way. I purchased a pump on EBay that was
rated at 25 inches but didn’t list the CFM. It didn’t have the strength
to hold a piece in the chuck. It was pumping like crazy but only got up
to 10 inches which, in my estimation, isn’t sufficient to hold the piece
to the chuck.
Therefore, you need to purchase a pump that combines both inches of
vacuum and CFM. You can go with the advice of the technical person I
spoke with and get a 25+ inches of vacuum and at least 4.5 CFM. I ended
up with a pump which I purchased on EBay which pulls 29 inches of vacuum
and has a CFM of 3.6, that pump works fine and I am very happy with it.
Let me spend a "few lines" of who I got it from. After my first
"disaster" purchase I hooked up with a person who buys vacuum pumps and
refurbishes them then sells the pump on EBay. The pump I purchased from
him had a slight problem which after 5 minutes on the phone with the guy
resolved the problem and the pump, to me, seemed to work just fine. But
the seller, Chris Martin, was listening, over the phone, to the pump
while it was running and made the determination that it didn’t sound
like it should have. He then said I should put the pump aside and he was
sending me another pump and that I should, once I receive the
replacement pump, return the first pump at his expense. He was so
apologetic that I had a problem and promised me that he would "make it
right". Chris called me a few days after I had received the replacement
to see how it was running and to make sure I was satisfied. WHEN WAS THE
LAST TIME ANYONE HAD DONE THAT ON AN EBAY SALE? It was the first time
for me. I wouldn’t hesitate to recommend him to anyone who wants to
purchase a vacuum pump. The pumps he sells comes refurbished as well as
powder coat painted and look like a new pump. The range of prices is
between $150 to $185 depending upon the CFM and inches of vacuum. You
can contact Chris Martin at 800-570-1130 or via email at
crisson62@hotmail.com.
2. Tubing and fittings
These are needed to get from the vacuum pump to the
lathe. There are a number of ways to approach your hookup. My first
attempt was to go onto EBay and key in vacuum chucks. Up popped a seller
that was selling all the fittings you needed to get from the pump to the
lathe including the tubing and a vacuum gauge. I purchase that kit but
used it with the pump that didn’t have the CFM to hold a piece on the
chuck. The best vacuum I was able to get was 10 inches. I wasn’t sure if
the size of the tubing which only had a ¼ inch inside diameter was big
enough for what I wanted to do. So I went to Home Depot and purchased
fittings, 3/8 inch inside diameter tubing and a sealed bearing and made
up a system that I felt was better.
I then was directed by Chris Martin, my pump guy, to a website
www.joewoodworker.com/veneering/vacuumchucking.htm
and found someone had done exactly what I ended up with and that seemed
to work well and was less money than what I spent, don’t forget to
figure in the cost of gas back and forth, a few times, to get what you
need. The price of the fittings from
www.VeneerSupplies.com
is only $44.25 plus they will attach the fitting that goes through the
bearing for only $10.95 more. The article on the link above really will
give you all the information you need to get from the pump to the lathe,
with two exceptions; the first is you should also put a dust strainer
between the hose going to the pump and the lathe. THIS IS VERY
IMPORTANT! No matter what you do you will be sucking in some sanding
or saw dust through the hose towards the pump. If you don’t strain out
the dust you will end up damaging your pump. You can use a regular
strain/filter that you can purchase at a good hardware store, i.e. Home
Depot or Lowe’s that would be used on an air compressor. Don’t forget
which direction the flow is coming from to that you make sure you have
the filter operating in the appropriate direction. The second exception
is to use a flexible sealant to glue the "O" ring onto the plastic so
that when you remove the bearing it doesn’t fall out.
As far as the hose is concerned, you can purchase it from any good
hardware store i.e. Home Depot or Lowe’s. Keep in mind you don’t have to
have the pump next to the lathe, all you will need is a switch to turn
it on and off. Chris puts a switch on the electrical cord. I have mine
sitting on a cabinet where I keep my sand paper and other turning tools,
next to my lathe.
3. The Chuck itself.
I first made my chuck out of wood, God knows, I have
enough of it hanging around my shop. You will either need to attach it
to a faceplate with a hole in the center or do as I did and went to:
http://www.use-enco.com then
under the "find it" at the top of the home page change from "keyword" to
"catalog page number" then input page no."36" and that would bring you
to the page for the specific type of tap. You then just pick you size
and thread. I have a Jet 1442 lathe which has a one inch – 8 thread.
Remember you are going to thread either wood and/or PVC (I will get to
that later) so you don’t need an expensive tap, carbon steel worked
well. The catalog price for 1 inch 8 thread is $5.30 for the tap plus
shipping. I think that the shipping was more than the tap. If you don’t
see the size you need just give them a call.
The tap had a square head and I used a wrench to tap the whole that I
made with a spade bit. Remember to use a spade bit that is smaller than
then the size of the finished hole. I am not saying that I drilled a
hole bigger than the tap. I drilled a 7/8 hole that was to big. You have
to remember that you will be cutting threads into the wood and a 1/8
inch differences isn’t enough. Drill a ¾ inch hole that you then can
tap.
I wasn’t smart enough, until I finished making my chucks, to realize
that I could make a tap holder out of wood by using a scroll saw to cut
an opening in the middle of a flat piece of wood then rounding the
"handles", think about an old style cork screw on either side of the tap
hole. Secure your tap in the hole with epoxy. That would have made the
tapping process much easier.
Let’s get back to making the chuck. You can glue up any scrap hardwood
to the size you want. Glue up a few pieces so you can have different
sizes. I have a 4" for large bowl chuck and a 2 ½" chuck for small
objects. You can probably find a wood turner who could turn your glued
wood into a cylinder, a little levity; if you can’t turn the cylinder
yourself you have no business making or even thinking of making a vacuum
chuck.
Now I am more interested in making larger and deeper bowls so I decided
that I would make my chuck at least 10 inches tall. I used my Talon
Chuck to hold the cylinder by cutting a foot in the wood cylinder while
it was between centers. Once the cylinder was in the chuck I again made
sure it was round. At this point I put the appropriate size spade bit in
a drill chuck which was mounted on an #2 Morse Taper in my tail stock. I
then turned my lathe down to the lowest speed and drilled a hole that
was ½" deeper that threaded portion of my lathe spindle. I locked my
tail stock and using the hand wheel on the tail stock to crank the bit
into the wood. Make sure you drill slowly and draw the bit out often to
clear out the shavings and let the bit cool. Once I was done I left the
cylinder in the chuck and with the lathe off, very important, I tapped
the whole just drilled.
After the hole was tapped I put thin CA glue on the cut threads and
allowed the glue to set up. After it dried I tapped it again and did
that process two additional times. Once completed, I then had a very
hard thread.
The next process was to mount the cylinder on the spindle. Turn on the
lathe and true the cylinder again. You should now dish out the top of
the cylinder at least ¾" inch leaving at least a rounded 3/8" rim that
is flat on the top. After that you will need to drill a whole completely
through the center of the cylinder. I drilled a ½ inch hole which
probably was overkill I am sure a 3/8 inch hole would be enough.
The next step is to seal the wood so there would be no chance of any
leakage through the cylinder wall. I used 5 minute epoxy which did the
job for me.
Now you need to put a "gasket" on the 3/8" cylinder rim which will seal
the bowl to the chuck. I purchased from Craft Supply a sheet of neoprene
rubber and glued up a piece that was 5/8" in width bigger than the chuck
using contact cement only on the rim. If you don’t get it perfectly
centered, don’t worry. All you need to do is turn on your lathe and
carefully insert a knife point into where you want the edge to be. I
would suggest you make the gasket size at least ¼ inch large than the
rim on both the inside and outside. You need to do this on both the
inside and outside so when you are done you have a "donut" gasket.
What I have found is that if you use your tail stock to help position
the bowl on the chuck WHILE THE LATHE IS TURNED OFF and you crank the
tail stock tight you may find that you will leave a black mark where the
gasket comes in contact with the bowl. I have solved that problem by
covering the gasket with plastic food wrap or a plastic bag with a hole
cut in the center. I wrapped the food wrap around the wood body of the
chuck and let it overhang the gasket. When I put the bowl on the chuck I
just make sure the plastic wrap is between the gasket and the bowl. Your
wooden chuck is now done.
I also decided to make a chuck out of PVC Pipe. I again burned $5.00 in
gas to go to HomeDepot and purchased a 4" PVC pipe fitting and a PVC Cap
which was the same ID as the fitting. I used a fitting because the rim
of the fitting is thicker than the PVC piping and would then give you a
thicker surface to glue the neoprene. They didn’t have a cap to fit over
the fitting. I turned a wood cylinder that would fit into the cap snugly
and was taller than the cap. That way I was able to force the pipe
fitting onto the wood and have it touch the cap. Then I put epoxy at the
joint and you now have a sealed chuck. I reversed the PVC chuck onto my
Talon chuck so I could drill the hole and then tap it to the spindle
size. Once you drill the hole you would want to check to see if there
are any gaps between the wood insert and the PVC cap where you drilled
the hole. If there are gaps use either Bondo or epoxy to fill the gaps
before you tap. After you tap do the same CA glue on the threads a few
times. Then do the same with the neoprene rubber on the rim. You are now
done.
4. Checking for leaks.
If you did a good job attaching the fittings using
Teflon tape and made a good seal where the bearing attaches to the High
Density Polyethylene (look at the picture above, you shouldn’t have any
leaks. For my lathe I purchased on EBay a plastic cutting board that was
1" thick. And glued a circle (cut on my band saw) which had a diameter
of about 3 ½ inches to the outside of the hand wheel using contact
cement. I then removed the hand wheel from the headstock and mounted it
in my Talon Chuck so I could "turn" the plastic to round (the plastic
cuts real easily with your turning tools and then drilled the center
hole to fit the bushing. Because I need to access the hole in the lathe
spindle from time to time to use a knock bar to remove a spur center, I
made a cap that could be easily remove so I could take the bushing out.
What I did for the cap was to take a piece of round Plexiglas that was
¼" thick, cut a hole to slightly greater than the diameter of the
fitting that holds the bearing, drill three holes in it so I could screw
the Plexiglas to the plastic material that holds the bearing. I mounted
the round plastic between all the fittings and the bearing. Needless to
say when you drill the hole for the bearing you need to be sure that the
bearing sits up slightly higher than the plastic attached to your wheel.
That way when you screw down the Plexiglas you will force the bearing
into the hole and make a good seal.
When I did mine I wasn’t able to get a good seal and had leakage. I then
cut a piece of neoprene to fit between the plastic cap and bearing and
that sealed the bearing in place and I ended up with virtually no
leakage from the pump to the bowl.
Your lathe might be set up differently then mine and you might have to
modify what I did to work on your lathe.
If you have any questions or suggestions as to
improving this article I would gladly accept your comments and I would
be happy to respond.
Mickey Goodman
mgoodman@tiac.net
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Posted Jan 2006 |
