Trouble with 1t arbor press

[DonCopal]

Hey,

 

I wanted to ask you for some advice as I'm having some trouble with my 1t arbor press. It's one of those standart presses from ebay and I modified it for my motors to fit under it. My motors are 15mm (I'm European), this is comparable to about 8 oz, I think. With 1t, it should be about 8000 PSI.

 

My problem is that while pressing motors, the bottom part of the arbor moves a bit to the front side so the rammer is a bit skew. Especially when I'm in the upper third of the tube, the effect is stronger. At the end, the tube is slightly bent. I think this due the the ability of the arbor to break to the sides a bit whhich can be adjusted using the screws. But even when I've tightened them as much as possible without getting the arbor stuck, the effect is weak but there.

 

I've once even destroyed the spindle of an expensive whistle tool because the tube had bent. Have you ever had such experiences ot can you give a an advice?

 

Also, I really dont know how much force I have to apply on the handle to reach the desired pressure. I don't have a force gauge. Do you know how to calculate that? ATM, I always press as hard a I can at the end of the handle, maybe this is too much?

 

BTW, I'm using a tube support made from a PVC pipe with a piece cut out vertically and several hose clamps.

 

Best regards

DonCopal

 

[mikeee]

DonCopal,

 

Most machines utilize a set of gibs (machined bar guides) to keep a desired movement in alignment.

Some of the cheaper machines may have set screws to align the movement and cheaper machines have nothing.

On your machine it looks like you might have (2) adjustment bolts on the front and (2) on the left hand side.

You might need to loosen (1) bolt and tighten the other bolt on each plane to change your alignment.

The other possibility is the riser blocks your press is sitting on, if all four corners are not the same height you

will have problems with alignment. You could use (4) stacks of washers the same size or (4) wrench sockets

the same size and height. The press also needs to be solidly bolted through the riser blocks to the bottom base

on the front and back side of the press.

[DonCopal]

Hi mikeee,

 

the corners all have the same height, the difference is just 0.01 mm or so. But maybe I can even erase that diff by using wrench sockets, thx for the idea!

[Col]

At the full 1 tonne (50kg on handle) you`ll have 6600psi on the comp, hollow rammers will exert more force as they have less area. Using a tube support can make all the difference at higher pressures.

Edited August 8, 2015 by Col

[DonCopal]

So 50 kg means on the end of the handle? How did you calculate that? Also, why 6600 psi? I calculated like this (sorry for using European system):

 

radius is 7.5 mm -> 7.5^2 * 3.14 = 176.625 mm^2

1000 kg / 176.625 mm^2 = 5.66 kg / mm^2

5.66 kg / mm^2 = 8048 psi

 

So, do you think it's ok when I press with good tube support as hard as I can or should I use a torque wrench or force gauge?

[Col]

Hi

Doing math late at night is fraught with danger Rechecked it (2204.6lbs on 0.2739 sq in) and you`re right 8048.658 psi. I cant imagine bending a tube in a support unless its thin pvc pipe or you`re not using enough clamps. I arrange them in a spiral so there`s no gaps.

You can make a force gauge for around 70 euro using a Sealey 5 tonne short bodied ram and a pressure gauge.

[mikeee]

A torque wrench is easily adapted to an arbor press which helps make consistent fuel grains.

[mikeee]

I have used solid tube supports on smaller motors and pushed them out with a solid rammer

after they are pressed. A pipe/tube is drilled to the correct ID for your motor tubes and the

inner surface is reamed and polished smooth to allow the motor to be easily pressed out

without causing undue stress on the fuel grain. A loose fitting tube can have a layer of paper

or mylar wrapped on the outside of the motor tube to make it fit snug in the solid tube support.

This type of support requires a hollow collar to stand the motor and support in while using a rammer the

same size of the OD of the motor tube to eject it from the solid support.

[DonCopal]

Maybe I have to use more clamps - I just use 4 or 5 for a 10 cm long tube. Do I really need more?

Also, do you think I could just use a piece of hardwood and drill a hole with the OD of the tube through it to make a support? Also, can you tell me why 50 kg on the handle?

Edited August 8, 2015 by DonCopal

[Col]

50kg x 20:1 ratio = 1 tonne.

I`d use as many clamps as you can fit, ensuring the slit in the support is closed when the clamps are tight. The tube can be forced into the smallest gap under high pressure. I assume your using good quality convolute wound tubes that cant be deformed by hand?

Edited August 8, 2015 by Col

[mikeee]

DonCopal,

 

If you use hard wood, make sure it is a solid hard, hard, hard wood.

You could make a clam shell with the wood and back it up with aluminum or steel flat plates and bolts.

I have used Corian counter top material and drilled a hole through several layers of the material.

Several layers can be glued together for the thickness needed and bolt holes drilled in it for a clam shell type support.

[DonCopal]

My tubes are good quality. When the clamps are tight there is about 5mm gap, does that really matter?

Edited August 8, 2015 by DonCopal

[schroedinger]

Yes that can be a problem. Also is your support 100% right angled?

 

I do 15 mm rockets too and had mainly bad results with using an arbor press. Using a hydraulic press or ramming have less catos. The problem i have is that the cheap presses don't really apply 1t.

[mikeee]

If your tubes fit loose in the support, wrap a short piece of craft paper the same size of your tube around it to take up the slack. Sheets of mylar or hard thin plastic also works.

Dave Forster in Canada uses thin brass metal shim material rolled around tubes as a tube support with good success. You have to wind the shim material onto the tube and use a clamp or rubber bands to hold the shim material rolled tight around your motor tube.

Edited August 8, 2015 by mikeee

[schroedinger]

Or get one of zmuros tube supports, cost about the same as brass shim and is ready to use.

[DonCopal]

what do you mean with "right angled"?

Edited August 8, 2015 by DonCopal

[mikeee]

DonCopal,

 

The bottom of your tube support needs to sit at a perfect 90 degree right angle on your rocket tooling base.

And your rocket tooling base needs to sit flat on your press plate to guarantee correct alignment with the ram.

Any of these not correct and you increase the chance of damaging your rocket tooling.

[DonCopal]

Ok, I'll apply all these tips and write then how it worked. Thanks!

[Mumbles]

Another way to help prevent the tooling from cocking to the side, particularly at the top, is to use a tubing extender. Some tool makers sell them, but they can be made from just a piece of the same sized tube, and something to hold it in place like a collar or extended support.

 

Here's an example:

http://www.firesmithtools.com/#/tube_extenders/

[DonCopal]

So I can just use another piece of tube and a pipe that fits tightly over it...quite easy. And how does that help?

Edited August 9, 2015 by DonCopal

[Mumbles]

It helps to keep things aligned. If there is some slight misalignment in your tooling or press, the additional support can keep things straight in some instances. As you get toward the top of the rocket casing, the torque applied by any misalignment adds up and you can start to damage tooling or the tube. The same technique is helpful for ramming as well. Any off center hits stay aligned and focused on the composition, not the tube or tooling.