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Press fits?

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a1cnolan

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Joined
Oct 11, 2001
Location
georgia
has anyone tried making blocks with a press fit? ive read a lot about leaks through the hose barbs and between the top and bottom of the blocks?i was just thinking a press fit is watertight. maybe one or two thousandths.... and then you could screw it together for extra measure...ahhh nevermind what if you had to clean out the inside....okay im dumb
 

frostmeister

Member
Joined
Jul 6, 2002
Location
Good old UK
What is a press fit? Do you mean the pipe fittings on the block? If you can describe them in a bit more detail, I/we might be able to give some more help... :)
P.S. - don't dismiss your own ideas out of hand and call yourself dumb, it may be a good idea :)
 

Albigger

Member
Joined
Sep 22, 2002
i dont' think a press fit of any kind would be water tight.

whether you are referring to press - fitting the hose barbs into the block?

or the top half into the bottom somehow?

either way, even if you just press fit a dowel pin into a hole, the hole is never perfectly round, so there is a possibility it would leak.

On the other hand i'm not sure how thin water flows, but I bet its less than .001" or so....
 
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a1cnolan

Member
Joined
Oct 11, 2001
Location
georgia
hmmm

definition of a press fit..
according to the mchinists handbook rev.24 a press fit is any fitting that has to be forced together through pressure. generally speaking 1 thousandth of an inch...so basically you make the top of the waterblock with a shoulder that will need to be pressed into a slot on the waterblock..kinda like a piece of a puzzle..

i was saying you could press fit the barbs and the top onto the bottom using locktite.... its a gear placing fluid that holds thing in place.it dries to make it very hard to pull things apart. also what kind of dowel pin wood. no thats not water tight or perfectly circular but using a lathe or a mill you can machine a perfect circle... and as for how thin water flows there would be no space for the water to go if there was space that would be a clearance fit. a press fit is the opposite the part you press into space is .001 larger than the thing your placing it into...


does that help any?
 

frostmeister

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Joined
Jul 6, 2002
Location
Good old UK
Yeah, I get what you mean now. You have to get those things pretty perfect, like you say, but there's no reason why a press fit should leak if done correctly. Another trick is to cool the thing which is bigger (pipe/barb, etc), and heat the thing which is smaller (hole/fitting) then push the two together. Due to thermal expansion, you then have a fitting which isvery hard to pull apart again if it's done correctly.
 

myv65

Registered
Joined
Mar 28, 2002
Press fits are a pretty routine thing, but not very common in the diameters you are discussing. The general rule of thumb for steel/steel is 0.001" per inch of diameter. With diameters under 1", the tolerances for an accurate press fit are very hard to obtain. Too high and you risk cracking the fitting, too low and it may not be stable and leak-free. Many engineering texts have the equations for determining interface pressure and the circumferential stresses in the mating parts. Unfortunately, all my books are at work.

At the very least, look into the equations a little as well as the properties of the metals. The rule of thumb applies to steel. Due to different elastic modulus and Poisson's ratio, the rule wouldn't necessarily work with copper, for example. Then look at how well you could actually control diameters. I think you'll find this impractical.
 
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a1cnolan

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Oct 11, 2001
Location
georgia
well the tolerances are not a problem.. i am going to cnc my waterblocks....i need to look at the effects of water on the locktite also...if not a press fit i may be able to use it to make the connection between the top and bottom better.

my thought was to make a shoulder on the top of the block. have an inset on the bottom and then have my maze below that...if it doesn't work no biggie.. i was pretty sure i couldn't do it with the hose barbs considering ill be using two different materials but actual block i thought it could be possible.....if i don't do a press fit im just gonna stick my block on a rotary table and go to work.okay thanx...later
 

Albigger

Member
Joined
Sep 22, 2002
First i agree with everything myv65 said. And secondly I also think it would be impractical to JUST do a press fit with lock-tite, some of the fluids you put in your system might corrode the lock-tite, so don't forget to look into that(you said you would already though)

also, i don' t know if you are doing a circular press fit or more of a rectangular one, but either way with the size you are talking it will be hard to make perfect. Even endmills and reamers don't cut perfect holes, so it doesn't matter all that much that you are doing it on a cnc, though you could get very close.

also, depending on the geometry/thickness of your block, if your fit is too tight you risk distorting the block (and possibly the flatness of the bottom) so don't forget to recheck this after you assemble the halves (if you end up doing it).
 
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a1cnolan

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Oct 11, 2001
Location
georgia
im just gonna scrap the idea...i was just trying to find a better way of making that seal
.. ill think of something... if i presized the thing i could have my sheetmetal friend bend some coppr tubing for the entire kit.damn i wish copper was weldable. id just weld the two halves together
 

frostmeister

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Jul 6, 2002
Location
Good old UK
Copper? Weldable? Any metal is weldable as far as I know, if you have the right tools. I'll let the engineering buffs already replying to your post elaborate on that one though :D . You could do what I did and solder the two halves together. My blocks have been running ok in my system for several months or so, no leaks - touch wood! All I did was solder 10mm central pipe into a brass plate and solder that to the top of the copper block. As long as you clean everything and use some decent flux, you're ok. The brass plate is 1 16th inch thick, and the copper pipe is a bit thinner; They're both rigid and have been fine in my experience.
 
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a1cnolan

Member
Joined
Oct 11, 2001
Location
georgia
i asked a guy in my shop.. he said as far as he knew no. but also if it were we don't have any copper welding rod in our shop.i can always silver solder the blocks together. i was actually considering getting the inside of my blocks silver plated for a while. i think that if i silver plate them the heat will be even more likely to got to where the water is and it should come off of the silver slightly quicker than copper. after all we all know that when it comes to cooling every little bit helps.

what i was saying earlier about using copper tubing i thought that would be awesome cause if it were weldable i would be able to weld up ever joint on it.... i do plan to weld up every hole in my case except the ones i want so i canc ontrol airflow better...
yeah i just got some artic silver 3 today.. yeah wouldn't believe it until you use it
 

JFettig

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Jan 5, 2002
Location
MN
this is interesting, i was just thinking about this seconds ago, just solder everything, to make it more interesting you should do brass tubing:)
 

frostmeister

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Jul 6, 2002
Location
Good old UK
Name change there Jfettig/masked ? :) Brass tubing... I've just been polishing up some brass plate on 1000 grit wetordry paper. Nice finish, except for a few scratches from earlier grades. So yeah, brass tubing anyway - I've got some lying around, but the thing is once it's soldered in place, you can't re-do it. And you've got to put bends and stuff in there. I got a pipe bender - basically a spring, and tried bending some brass pipe - way to difficult to be practical. Nice thought though, I'd love a "traction engine" style PC with rivets, brass and copper tubing and maybe a guage or two... Might be quite a good mod - retro in the victorian style - similar to machines and inventions in the bitmap brothers "chaos engine" on the amiga - years back...
 

JFettig

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Jan 5, 2002
Location
MN
If i didnt change stuff soo often, i would do it.... or if i had a deadicated system to do it on...

edit- name change, yes...