5c collet chuck

[kd0afk]

Do they make 1-1/2"-8 helicoil?

 

[kd0afk]

I discovered the mistake I made. I ground the threading tool from a old brazed carbide bit but didn't grind enough clearance. Rookie mistake.

 

[Swifty]

I have the steel to do that. Probably thread it and use permanent locktite right?
I'm just sick about this.

Would be best to loctite and pin it some way, then you are not just relying on the loctite to hold when tightening up the collets.

Paul.

 

[kd0afk]

Andrew suggested that I bore out the hole and make a plug thats .001" over and do a shrink fit. He said it wouldn't budge and pretty invisible. I was thinking of buying a backplate from shars but their 5" plate is $45. I have steel and a torch I'll try the plug first.

 

[kd0afk]

I looked up the numbers for thermal expansion of cast iron. It said the temperature range is 32-212 F and 5.8 microinches /inch F.
I have no idea what that means. Can anyone explain it?

 

[Swifty]

I looked up the numbers for thermal expansion of cast iron. It said the temperature range is 32-212 F and 5.8 microinches /inch F.
I have no idea what that means. Can anyone explain it?

I think that the expansion is probably measured on a straight piece a foot long. It's a bit hard to work out how much a round piece with a hole in the middle is going to expand.

If I was going to do it, I would make the insert about .001" / .002" bigger on diameter, put the outer piece in the oven for 30 minutes at nearly it's highest setting, when ready grab the outer with oven mitts and place it over the waiting insert. (Don't do this on the kitchen bench / counter top). I usually have the insert sitting on a steel plate, make sure everything is square when you put them together.

Disclaimer: all advice given freely, but no responsibility .

Paul.

 

[kd0afk]

Will 2" dia be ok for the insert? The spindle is 1.5"

 

[mu38&Bg#]

With a thermal coefficient of expansion of 5.8 microinches per inch per degree Fahrenheit, a piece of cast iron 1" long at 70°F would be 1.000005.8" long at 71° So if you want to shrink fit you'd have 2" at 70°F and 2.00104" at 250°F or 2.00209" at 430°F. If you make the interference too great, the cast iron can crack. Shoot for .001-.002" of interference as suggested. Measure the bore and insert carefully and make sure the parts have a good surface finish. Putting the insert in the freezer gives you a bit of extra clearance to get things assembled. Once you begin sliding these together you will be committed.

On my Lathe rebuild I heated up a bearing and slipped it into place on the spindle. About 1 millisecond after the bearing grabbed the shaft, I realized I forgot to slip on a part that goes on before the bearing. Unfortunately this bearing is up a against a large shoulder with less tham 1mm behind the race. I had to make a puller to remove it.

Greg

 

[kd0afk]

So, 2" should be big enough right? It will have 1/4" of material around the threads. Also, lets say, the surface finish is good on both parts and the insert is frozen and the iron is at 500F, how much time am I going to have to mate the two before they lock up? Milliseconds doesn't sound like a good margin for error.

 

[ddmckee54]

You're going to have to get out your algebra and maybe even your calculus to figure that one out. If you know the exact size at ambient temperature, and you know the temperatures that you are heating and cooling the parts to, then you can calculate the clearance that you will have the instant you start to put them together. Then you find the heating/cooling rates of the material and calculate how long it will take for that clearance to go away. Let's just say you don't want to dilly-dally around if you want everything in the right place.

Don

 

[kd0afk]

It's going to be; backplate from the oven to the steel plate on the floor and at the same time plug from freezer to backplate. Shouldnt take but seconds. Still nervous about it.

 

[Swifty]

It's not for the faint hearted, you have to work quickly as it can grab in no time.
Have the plug ready before you get the backplate from the oven, don't put the backplate on the floor first as you will lose heat straight away.

Paul.

 

[kd0afk]

I just remembered that I have a big cast iron skillet. I think I'll put both in the oven so the backplate won't cool down so fast.

 

[kd0afk]

I got the plug finished and it fits like it was meant to go on there. But I'm stuck till I can find my strap wrench. Oh well. I threaded the plug and machined the shoulder and then screwed it on to the spindle to true up the outside and I can't get it off now.

 

[mc_n_g]

Trepanning sounds better and better from the beginning.
You have opened a whole new can of worms, but you are working through it.

 

[kd0afk]

Trepanning sounds better and better from the beginning.
You have opened a whole new can of worms, but you are working through it.

The plug I'm making has nothing to do with the trepan. I've still got to cut the trepan plug but the threaded insert is because I screwed the pooch on the backplate.
I'm machining the hole to accept the insert today.

 

[kd0afk]

Looks like I'll be buying a new backplate. I cut the hole in the plate too large. I don't know how, I was extra careful but something happened. found one for a boxford lathe that will work for less than $30

 

[kd0afk]

This was a huge learning project.
There are a few more things I need to do to complete this. Bore and thread the nut, mount the ball race slug, machine all the bearing groves, drill and tap for the key and drill the tommy bar holes on the back end and she'll be ready to use.
I can't draw it in tight but I put a dti on it and it read .00015 tir. For my first complex project I think I did pretty well. I think also that once I'm able to draw the collet and tighten the nut the tir might go down a bit. The bore was machined in-situ so maybe it's the collet, I don't know at this point. I do know that the thing is a bit more accurate than my three jaw.

 

[kd0afk]

I will probably be making a new nut when I get a new caliper. Somehow the thing wasn't true to it's own axis when I machined the grooves and holes. The slots are askew and the holes don't completely line up. No problem though I have the extra stock and I know how to correct the error.
All in all this was a fun project and I think I'll get some good use out of it.

 

[mc_n_g]

Happy to see you enjoyed it even though you had a few problems. Part of learning.
Hope the rest of it comes out ok for you.
Once you complete it and use it you will be happy with the results.
The accuracy is a very nice addition.