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Making a DRAW TUBE for hydraulic chuck.........where to start

bil99

Plastic
Joined
Jul 9, 2023
Hello everybody
I need a new drawtube for my Hyundai hit 8, its 618mm x 42mm x 4.5mm wall and i have no idea what to make it from, the more i read about metal grades
and specs the less i know, i have read that i need 1026 DOM tubing which i cant find with a 33mm ID bore.
The best i found so far was 45mm x 35mm tubing used for making hydraulic cylinders thinking i can trim the OD to 45mm and insert a piece of 35mm x 1mm SS tube inside it
to bring it down to 33mm to match my plastic liners
Will it need heat treated or hardening after machining, will it bend or stretch if used as is?
Has anybody made one before
Some might ask why i dont buy one..........quote i got from uk supplier was £729.60, 14 to 28 days for delivery
and yes i am based in the uk
Drawtube.jpg
 
By the time you order material, machine it, order new material because the first one ended up scrap, heat treat it (if needed), make the third one because the thin tube warped in HT, make the fourth one because old Eagle-Eyed Joe misread the 816mm line on his tape measure - how far ahead will you actually be on a $1000 part?

That being said, 4140 is just about my favorite material to make just about anything important with. Not too expensive (At least in the US), can be ordered pre-hardened, machines nicely, and is pretty sturdy stuff. 4130 (aka Chromoly) is another option that's pretty commonly available in tubes (again, in the US). Not sure how common anything with a 33mm ID is anywhere though.

The "will it stretch?" is a stress calculation. Drawbar force divided by cross sectional area, account for the stress concentrators at the weakest point (probably at the steps or threads) - compare the load stress with the yield strength of the chosen material to see if it's likely to rupture. I think Machinery's Handbook or any good engineering text can give you more info on that.

Disclaimer: I'm not responsible if your drawtube gives up the ghost and lets a 2 lb chunk of 12L14 fly out of the spindle through the safety glass and into the foreman's coffee mug
 
We have purchased drawtubes and had to cut a bit of the length off to make them work. They are not hard.
 
$1000 just order the damn thing. If you were going to go for a bush fix I would weld a replacement chunk on the end and machine OD and ID to match.
 
The tube ID is your limiting factor, if you source a piece of tubing to make your own drawtube. Tubes of a given OD will have different wall thicknesses, which determines the ID of course.

You can skim the OD if needed to fit your machine's spindle with some clearance.
Any decent grade of steel tubing will work, make sure to use threading inserts with the correct nose radius, to maximize strength of the threads.

I would want at least .150" wall thickness tube for an 8"/10" chuck machine.
 
1 - 1/4 schedule 80 seamless pipe? 0.007 oversize on od and 0.021 undersize on the ID. If the ID is critical then no go as I can't see reaming a 24" long tube with a 1.299 (33mm) reamer. But if its close enough you might be ok. I think finding 1-1/4 schedule 80 in 4140 might be tough, but if the original spec is 1026 plain old pipe may be ok. I was reading that DOM is a bit softer than plain old pipe.

BTW, what was the failure mode of the last drawbar?
 
1 - 1/4 schedule 80 seamless pipe? 0.007 oversize on od and 0.021 undersize on the ID. If the ID is critical then no go as I can't see reaming a 24" long tube with a 1.299 (33mm) reamer. But if its close enough you might be ok. I think finding 1-1/4 schedule 80 in 4140 might be tough, but if the original spec is 1026 plain old pipe may be ok. I was reading that DOM is a bit softer than plain old pipe.

BTW, what was the failure mode of the last drawbar?
Im only guessing from the marks on the back of the chuck that the previous owner bolted the chuck onto the top of the
locating dowel leaving it at a slight angle to the backplate, then when the hydraulics pulled the tube, the nut applied more pressure to one of the jaws than the other two and bent the tube.
I set the tube in v-blocks with the nut on and theres 0.9mm gap between the face of the nut and the v-block on one side
 
The tube ID is your limiting factor, if you source a piece of tubing to make your own drawtube. Tubes of a given OD will have different wall thicknesses, which determines the ID of course.

You can skim the OD if needed to fit your machine's spindle with some clearance.
Any decent grade of steel tubing will work, make sure to use threading inserts with the correct nose radius, to maximize strength of the threads.

I would want at least .150" wall thickness tube for an 8"/10" chuck machine.
Its a 6" chuck and closest i can find is 45mm tube with 5mm wall leaving it 35mm honed ID
maybe i can sleeve it with a piece of 35mm x 1mm SS pipe
 
I've subbed deep hole boring / honing to Hone All Precision in the UK in the past and have found them to be reasonable. You could get the exact bore you need then and not have to shim the drawtube. That being said, by the time you source the pipe / bar and live with their delivery plus machine the threads on the end (they haven't been that keen to machine ports on the bores they've done for me in the past) the price quoted for the replacement would probably seem pretty reasonable.

I was chatting to the guys over at 1st MTA when I ordered my collet chuck from them and they said they use any old mild steel for the thread adapters so I would assume the same would be suitable for the draw tube. I was going to make one out of 4145 as I had some on the shelf but decided to get their mild steel one just to save a bit of time.
 
By the time you order material, machine it, order new material because the first one ended up scrap, heat treat it (if needed), make the third one because the thin tube warped in HT, make the fourth one because old Eagle-Eyed Joe misread the 816mm line on his tape measure - how far ahead will you actually be on a $1000 part?

i will be much more experienced after the fourth one, just like you, and then probably pay $1000 for a new one
:D:D:D:D
 
I've subbed deep hole boring / honing to Hone All Precision in the UK in the past and have found them to be reasonable. You could get the exact bore you need then and not have to shim the drawtube. That being said, by the time you source the pipe / bar and live with their delivery plus machine the threads on the end (they haven't been that keen to machine ports on the bores they've done for me in the past) the price quoted for the replacement would probably seem pretty reasonable.

I was chatting to the guys over at 1st MTA when I ordered my collet chuck from them and they said they use any old mild steel for the thread adapters so I would assume the same would be suitable for the draw tube. I was going to make one out of 4145 as I had some on the shelf but decided to get their mild steel one just to save a bit of time.
Nearest ID i can get is 35mm and i need 33mm so honing wont help and the sleeve wont add any strength, its only to fit the plastic spindle liners, maybe i should use the 35mm and make new liners
 
Specs for material ive found sofar
 

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Nearest ID i can get is 35mm and i need 33mm so honing wont help and the sleeve wont add any strength, its only to fit the plastic spindle liners, maybe i should use the 35mm and make new liners
They can drill a hole through solid and hone to tighter tolerances if required is what I was meaning. New liners would probably be the easiest way, plus you'd get a tiny bit more spindle capacity which could come in handy. I would have thought the wall thickness would be alright based on the draw tube on my HAAS being a lot less than 4.5 mm although I couldn't tell you what it actually is without removing the chuck.
 








 
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