Suggestions for making 3 concentric axles

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21st August 2014, 10:12 PM
bloodandsawdust

Suggestions for making 3 concentric axles

Greetings.

I want to build a large orrery (mechanical display of the planets orbits, google it) and I find that I need 3 independant rotating motions on the one axis. This is usually done in orreries with precision telescoping brass tube, like from K&S from hobby shops, but what I am building is large, and heavy, a few kilos, but rotating very slowly, the fastest will be 1 rpm. The axis is vertical, most of the load is vertical but the drive will give a bit of side force. Since I have no lathe (but I do have a drill press) most of my work is with steel and I tend to weld things together a lot, just with tacks if I might want to dismantle it one day.

What I am thinking is to use the black industrial pipe available from steel suppliers 15NB, 20NB & 25NB (medium wall thickness) (OD's 21mm, 27mm, 34mm) which from the pipe tables are a reasonable fit inside each other, maybe 0.5mm clearance, and just grind off the high spots until I have tubes that all turn with no binding. Is there any reason why this won't work? Then lots of dry lube to keep it turning freely (grease attracts dust which turns to grinding paste).
21st August 2014, 10:57 PM
Uncle Al

Assuming you only need short lengths of each pipe, try and get some offcuts of seamless pipe from a pipe fabricator who works for the oil or chemical industries or maybe hydraulic pipe people. The alternative is ERW pipe (electrically resistance welded), but this will have a bit of an internal seam which may cause you problems. Seamless pipe is used where the end user will not take the risk of a welded seam letting go (most unlikely, but I have seen it happen). Both pipes have the same general dimensions and pressure rating, but most oil refineries in Australia won't use ERW pipe in critical areas, and some won't use ERW on their site unless it is galvanised and therefore easily identified and then only for water or air reticulation.

Good luck with your project,

Alan...
21st August 2014, 11:04 PM
Oldneweng

Quote:

Originally Posted by bloodandsawdust

Greetings.

I want to build a large orrery (mechanical display of the planets orbits, google it) and I find that I need 3 independant rotating motions on the one axis. This is usually done in orreries with precision telescoping brass tube, like from K&S from hobby shops, but what I am building is large, and heavy, a few kilos, but rotating very slowly, the fastest will be 1 rpm. The axis is vertical, most of the load is vertical but the drive will give a bit of side force. Since I have no lathe (but I do have a drill press) most of my work is with steel and I tend to weld things together a lot, just with tacks if I might want to dismantle it one day.

What I am thinking is to use the black industrial pipe available from steel suppliers 15NB, 20NB & 25NB (medium wall thickness) (OD's 21mm, 27mm, 34mm) which from the pipe tables are a reasonable fit inside each other, maybe 0.5mm clearance, and just grind off the high spots until I have tubes that all turn with no binding. Is there any reason why this won't work? Then lots of dry lube to keep it turning freely (grease attracts dust which turns to grinding paste).

I made a cement mixer using pipe inside pipe for the drum pivot and rotation, many years ago. It still works perfectly. I have seen tables from steel manufactures that list various sections which fit inside others for sliding fits. What I remember was square section from memory, but I am sure the same would be available for round tube/pipe.

Dean
21st August 2014, 11:43 PM
.RC.

The ID of your standard pipe is not smooth, as the welded seam protrudes inside..
22nd August 2014, 12:36 AM
rogerbaker

Brass Tubing

Go see George White in "Springvale"( or somewhere near there). They will have heavier brass tubing than the hobby stuff.

Roger
23rd August 2014, 03:28 AM
bloodandsawdust

Quote:

Originally Posted by rogerbaker

Go see George White in "Springvale"( or somewhere near there). They will have heavier brass tubing than the hobby stuff.

Roger

I know George White. Where I work we design industrial power supplies and the workshop guys are always popping over for some copper shim or sheet. I have bought lots of scraps from their scrap bin in the past.

However whilst having brass sleeves would be a very good solution, the project is for a rural sculpture contest where the materials should be as found on the farm. Steel pipes are believable, but brass would just look too good. Besides the rest of the creation is steel, and I don't want to be brazing as I don't have a torch.

So thanks for the idea.

TomH
23rd August 2014, 03:32 AM
bloodandsawdust

Quote:

Originally Posted by .RC.

The ID of your standard pipe is not smooth, as the welded seam protrudes inside..

Aha! I learnt a trick from a farm mechanic to fix this little problem. Put a length of rod in your drill chuck. Tie a bundle of rags to the end slightly larger than the pipe. Then tie some strips of very coarse emery paper (40g) to the rod so that they hang over the rags. Then run it up and down the pipe a few times. Cuts off that pesky seam.
23rd August 2014, 03:34 AM
bloodandsawdust

Quote:

Originally Posted by Oldneweng

I made a cement mixer using pipe inside pipe for the drum pivot and rotation, many years ago. It still works perfectly. I have seen tables from steel manufactures that list various sections which fit inside others for sliding fits. What I remember was square section from memory, but I am sure the same would be available for round tube/pipe.

Dean

Well that's very encouraging. A cement mixer uses lots of sand, so if it was going to wear out it would. Did you run it dry with no lube?
23rd August 2014, 03:36 AM
bloodandsawdust

Quote:

Originally Posted by Uncle Al

Assuming you only need short lengths of each pipe, try and get some offcuts of seamless pipe from a pipe fabricator who works for the oil or chemical industries or maybe hydraulic pipe people. The alternative is ERW pipe (electrically resistance welded), but this will have a bit of an internal seam which may cause you problems. Seamless pipe is used where the end user will not take the risk of a welded seam letting go (most unlikely, but I have seen it happen). Both pipes have the same general dimensions and pressure rating, but most oil refineries in Australia won't use ERW pipe in critical areas, and some won't use ERW on their site unless it is galvanised and therefore easily identified and then only for water or air reticulation.

Good luck with your project,

Alan...

Thanks, I'll ask around. I'm off to the scrappie tomorrow, see what he has lying around. At least I know what to ask for now!
23rd August 2014, 05:46 AM
bloodandsawdust

Quote:

Originally Posted by Oldneweng

I made a cement mixer using pipe inside pipe for the drum pivot and rotation, many years ago. It still works perfectly. I have seen tables from steel manufactures that list various sections which fit inside others for sliding fits. What I remember was square section from memory, but I am sure the same would be available for round tube/pipe.

Dean

Found the table for black pipe, they are in the old Blackwoods catalogue. I knew that I had hung on to it for a reason!
23rd August 2014, 09:52 AM
Oldneweng

Quote:

Originally Posted by bloodandsawdust

Well that's very encouraging. A cement mixer uses lots of sand, so if it was going to wear out it would. Did you run it dry with no lube?

No, I used a ~~zirk~~ sorry, grease nipple in the middle of each section. The first time I had used a grease gun in years was when I got the mixer ready to cement the lathe foundation. Grease nipples are very "rural" and the grease sitting at the ends will keep out any dust.

Dean
23rd August 2014, 10:56 AM
.RC.

Quote:

Originally Posted by Oldneweng

The first time I had used a grease gun in years was when I got the mixer ready to cement the lathe foundation.

Reminded me of

Quote:

Originally Posted by krisfarm

I have a mate that has a general engineering repair shop and he often shows me the sort of jobs he gets in, a lot of earth moving, dump truck etc.He tells me that they mostly fall into one of two groups.They do not own a grease gun or they own one and never use it again after the first cartridge is empty.

:D:D
24th August 2014, 07:09 PM
bloodandsawdust

Quote:

Originally Posted by Oldneweng

No, I used a ~~zirk~~ sorry, grease nipple in the middle of each section. The first time I had used a grease gun in years was when I got the mixer ready to cement the lathe foundation. Grease nipples are very "rural" and the grease sitting at the ends will keep out any dust.

Dean

That is such a good idea Dean. Low tech solutions I like. Agricultural engineering used to have lots of grease nipples, when I was young I did a week helping a farm mechanic, he was so keen on his grease gun that was his nicname "greasy". Since I have concentric axles I shall make a cross hole to allow the grease to flow in to the inner axles.

I have just spent the day making the axles run nicely, I made a hone with a very powerful Sher drill (Aussia made!) with a rod with floor sanding paper wrapped round it to clean up the insides of the sleeves until they all ran true. Then it started raining.

Thanks for the help!