Cylinder with a hole in it - suggestions?

[tetsujin]

One of the parts I need to make is a cylinder (9.5mm diameter, 7mm length) with a 5mm hole through it, on-axis.

My first attempt was based on using telescoping thicknesses of styrene tubing, starting at 5mm inner diameter and ending at 9.5mm outer diameter. This didn't work out so good, the inner hole was off-axis.

Second attempt was based on two bits of telescoping tubing, built up to the inner diameter of the 9.5mm tubing, spaced apart and used as a guide to make a third in between the two. This approach was basically garbage in, garbage out - averaging out the errors between the two flawed parts didn't give me better precision.

Third attempt - and probably the best so far, was based on constructing the part around the axis using polyester putty, and then spinning it on the Dremel to smooth it out and get it down to size. This approach seems partially successful - at least better than anything else I've got so far... It still seemed to have a little wobble when I spun it, though...

I suppose I could do something like photo-etch a couple of discs and build up the cylinder between them, or something - if I ever actually get around to doing some photo etch... Any other suggestions?

[Andrew Gorman]

I'd go to a good old fashioned hardware store and see what they had in the way of stock bushings or sleeve bearings. If your dimensions aren't set in stone there should be something that will work in steel, bronze, or nylon.

[tetsujin]

I'd go to a good old fashioned hardware store and see what they had in the way of stock bushings or sleeve bearings. If your dimensions aren't set in stone there should be something that will work in steel, bronze, or nylon.

Inner dimension would have to be 5mm or 3mm pretty much exactly, or I can't fit it to the axis I need to use... Length is negotiable, maybe outer dimension a bit as well...

[Andrew Gorman]

1/8 or 3/16 bore should be easy to find and could work.

[Mark Yungblut]

Two possibilities for you...

First look around at local hobby shops and see if any have the aluminum tubling modelers use all of the tubing is designed to telescope.

The other option is to find the right size OD tube and fill it with a hard epoxy putty like Aves. once cured drill a pilot whole in the center and keep stepping up the diameter of the drill bit until you hit 5mm. Many US hardware stores carry a set of metric drillbits.

Oh and if you have a drill press or access to one I recommend usin it to drill the center hole.

Cheers,

Mark

[tetsujin]

Two possibilities for you...

First look around at local hobby shops and see if any have the aluminum tubling modelers use all of the tubing is designed to telescope.

I had thought about this - but was concerned that it'd end in the same problem as with the styrene tubing - that cumulative precision errors as the number of layers increases would kill the precision of the thing... Compared to the styrene tube, the basic tolerances would be a lot better (metal being a more sturdy material, and the telescoping diameters matching more precisely than with the styrene) but there would be more layers, too.. Still, it's probably worth dropping a few bucks on metal tubing to give it a try...

The other option is to find the right size OD tube and fill it with a hard epoxy putty like Aves. once cured drill a pilot whole in the center and keep stepping up the diameter of the drill bit until you hit 5mm. Many US hardware stores carry a set of metric drillbits.

Oh and if you have a drill press or access to one I recommend usin it to drill the center hole.

How does one ensure that such a hole is really on-center? This is to be a moving part, so even a minor deviation would be pretty noticeable. Honestly, I've had enough trouble just getting the cut end to be really perpendicular to the axis - that, of course, would be a necessary first step before attempting to drill the hole.

1/8 or 3/16 bore should be easy to find and could work.

1/8 is larger than 3mm - I would need to center the 3mm rod within the part. Still, it may be a good starting point...

[Kylwell]

A center square helps with getting a good center.

[futch]

drill press or a dowel jig. you could make your own jig - i've done it before out of wood and a metal bushing.

another idea is to drill part-way into a length of solid plastic tube or wooden rod with a 5mm bit. take the tube out of the vice but leave it on the drill bit. use your drill like a lathe to bring the outer dim down. when the outer dim is finished, finish drilling the hole. cut to length.

[Chacal]

One of the parts I need to make is a cylinder (9.5mm diameter, 7mm length) with a 5mm hole through it, on-axis.

As I gather you have the 5mm inside diameter and the 9.5mm outside diameter tubes, right?

Start with a length of the 5mm (one inch or 25mm—actually it has to be some 20mm more than the width if the tape. What tape? Read on). Start wrapping tape around one end of the tube, the thinner the tape and the tighter the wrapping, the better. Keep going until the diameter of that 'lump' (more of a cylinder) of tape fits nicely, if tightly, inside the 9.5mm tube (which will be some 5mm shorter than the thinner tube). Fit them one inside the other. You will have a double walled tube. Apply thick, gooey putty to the anullus (the space between the tubes) from the side without tape. Before the putty sets, make sure the free end (the one without the tape) has the tubes properly centered (the tape side will already be centered if the tape was well wrapped).

After the putty sets, use a razor saw to cut a 7mm slice off of the tubes (actually, cut a bit long then sand the ends nice and square).

[tetsujin]

Start wrapping tape around one end of the tube,

Ah, should have thought of this one... I've certainly heard of this method before but never tried it... Maybe this is my next attempt...