Cutting a keyway ?

[W.olly]

I am still trying to sort this out. Now i snapped the threaded end off the what i think is an inner tube for the worm gear shaft.

This tube has an ID of around 25mm with full length keyway and is around 120mm long.
I am thinking this is an inner tube as i cant see the housing being machine to such tight tolerances for a key way to be done. Maybe i am wrong ?

What i hope is that this is an inner tube of the casing for for the worm gear to slide.

the housing

the snapped off threaded end

the other end with a bearing carrier

So if that is an inner tube in the housing and i can press it out, what are chances of if i make the tube somebody will want to cut the key way for me, or anybody knows of a person to do so ?

Just working out best way to go.

 

[Agroshield]

Remove the bearing carrier and look under it. Chances are it is one piece. Having an inner sleeve offers no benefits to the manufacturer or the end user and adds a huge amount of cost and complexity. The casting would likely have been cast solid and the hole bored and then keywayed. Being so long, it could have been done with a pull broach.

I am not sure why you think the whole keyway needs recutting. The very critical question is: if the keyway is lost from (or, rather, is greatly oversize on) the short length of threaded part at the bottom during a repair, what are the consequences?

To repair, face off and turn down the end where the thread goes (possibly easier on a mill with a boring head than trying to chuck the lump up in a lathe). Make sure the exterior turned down bit is very concentric with the inside bore. Prepare a lump of cast iron that is a shrink fit over what you have turned down with the rest of it looking like the missing thread. Put a nice radiused relief groove at the base of the thread as the old one looks to have a sharp corner. Make the bore in it maybe 0.5mm smaller than the existing bore. Shrink it on. Cross pin it for security. Ream it from the far end to finalise new bore diameter and to correct any slight closure of the old bore due to the shrink fit.

If the size and alignment of the short bit of keyway that has been lost is critical, you can use a standard push broach to reform the short bit of keyway that has been lost. The challenge is in aligning the new bit with the old - you could put a not-too-tightly-fitting piece of keystock into the old keyway and use it to align the bushing. Then you clamp the bushing from rotating. The end of the broach should then push it forward out of the way.

 

[W.olly]

Remove the bearing carrier and look under it. Chances are it is one piece. Having an inner sleeve offers no benefits to the manufacturer or the end user and adds a huge amount of cost and complexity. The casting would likely have been cast solid and the hole bored and then keywayed. Being so long, it could have been done with a pull broach.

I am not sure why you think the whole keyway needs recutting. The very critical question is: if the keyway is lost from (or, rather, is greatly oversize on) the short length of threaded part at the bottom during a repair, what are the consequences?

To repair, face off and turn down the end where the thread goes (possibly easier on a mill with a boring head than trying to chuck the lump up in a lathe). Make sure the exterior turned down bit is very concentric with the inside bore. Prepare a lump of cast iron that is a shrink fit over what you have turned down with the rest of it looking like the missing thread. Put a nice radiused relief groove at the base of the thread as the old one looks to have a sharp corner. Make the bore in it maybe 0.5mm smaller than the existing bore. Shrink it on. Cross pin it for security. Ream it from the far end to finalise new bore diameter and to correct any slight closure of the old bore due to the shrink fit.

If the size and alignment of the short bit of keyway that has been lost is critical, you can use a standard push broach to reform the short bit of keyway that has been lost. The challenge is in aligning the new bit with the old - you could put a not-too-tightly-fitting piece of keystock into the old keyway and use it to align the bushing. Then you clamp the bushing from rotating. The end of the broach should then push it forward out of the way.

The key way is a guide for the key all the way down the tube. And all that is beyond my capabilities, aswell as the gear to do it. If i cant get the part it need ( at an affordable cost ) to replace it i will have to get it machined.

thanks for the input kida

 

[8ob]

As the flange is also broken get the flange with the short tube/thread/keyway made up in steel with a spigot towards the casting and machine the casting to take that spigot, then press them together and furnace braze them.

Bob

 

[Brad93]

How long is the keyway and what width is it?

 

[8ob]

How long is the keyway and what width is it?

It goes all the way through Brad.

 

[pressbrake1]

Pull broach or key seater job which are rare so I reckon wire eroding if you have the budget and find a machine with enough throat height

 

[Agroshield]

The key way is a guide for the key all the way down the tube.

Have a good look at the diagram 8ob posted. The keyway has been made the full length of the tube because making a blind keyway is ten times more difficult than making a through keyway.

The critical question is how much of that length does the key itself use or need?

When the 'screw spindle set' in the diagram is fully extended, does the woodruff key actually go into that part that is broken? When the 'screw spindle set' is fully retracted, where is the key in relation to the top of the bore? Does it hit the underside of the lower bearing race?

If the key itself never reaches the broken bit at full extension, you are in the clear. If it overlaps it for the full length of the key, maybe a longer key (so that its extended part stays in the old bore) could work so long as it does not cause aggro. at the top. If it overlaps it only a little, what is the effect of limiting the travel of the 'screw spindle set'? If you had to limit the travel, which has least bad effect: limiting the extension or limiting the retraction? What do you lose if the range of adjustment is a little less in one direction or the other? If there is space at the top of the bore, but a problem at the bottom, maybe you can move the key upwards in the shaft to overcome the problem.

 

[W.olly]

Have a good look at the diagram 8ob posted. The keyway has been made the full length of the tube because making a blind keyway is ten times more difficult than making a through keyway.

The critical question is how much of that length does the key itself use or need?

When the 'screw spindle set' in the diagram is fully extended, does the woodruff key actually go into that part that is broken? When the 'screw spindle set' is fully retracted, where is the key in relation to the top of the bore? Does it hit the underside of the lower bearing race?

If the key itself never reaches the broken bit at full extension, you are in the clear. If it overlaps it for the full length of the key, maybe a longer key (so that its extended part stays in the old bore) could work so long as it does not cause aggro. at the top. If it overlaps it only a little, what is the effect of limiting the travel of the 'screw spindle set'? If you had to limit the travel, which has least bad effect: limiting the extension or limiting the retraction? What do you lose if the range of adjustment is a little less in one direction or the other? If there is space at the top of the bore, but a problem at the bottom, maybe you can move the key upwards in the shaft to overcome the problem.

The key way is full length so the shaft is guided through so the shaft can full extend as in pictures.

The way its going I have found two for sale. One in americanised for £170 ex postage. And one in Denmark. Jusr waiting on a price. Most on the net I ja e found have been around and about £1000

 

[W.olly]

Happy days

Somebody has sent me one for £60

bloody bargain

 

[addjunkie]

Happy days

Somebody has sent me one for £60

bloody bargain

Dont break it!

 

[W.olly]

Dont break it!

lol, this time i know how it comes apart so wont be tw£££ng as much haha.

Ill soak this for a week aswell in diesel to make dam sure if come apart easier.

Getting the top cover off is not so easy either, even with loads of heat. snapped two chain wrenches on one of them, just ordered a HD one.