Distortion Of 4130 Round Stock?

[fvdbergh]

I am planning on turning a D1-4 camlock backplate for my lathe. In the past, I have made an ER20 collet bar (that I just hold in the 4-jaw) using 4130 in the annealed condition, as well as an MT-2 gear cutter arbor, and I was quite happy with the way it machined.

This time round, I am considering buying the 4130 (actually, EN19) in the "pre-hard" condition, which should be about RC30, which still sounds easy enough to turn. I mostly hope that the harder condition will last longer in its role as D1-4 backplate, but I suspect that even in the annealed condition the 4130 will be adequate.

Then I saw a recent video by John Grimsmo where he briefly showed a part that was machined from 4130 (plate stock, I assumed), which distorted quite badly (just from the machining, no HT). I suspect that plate stock 4130 is probably cold-rolled, which would explain the distortion (considering the anisotropic grain structure that would result).

Finally, my question: should I worry about similar distortion when turning a large part (such as the D1-4 backplate) from round stock, in either the annealed or "pre-hard" condition? Or is the grain structure of the bar stock still relatively isotropic?

 

[Uglydog]

I've no answer. But, I'm eager to watch this thread!!

Daryl
MN

 

[f350ca]

Anytime you remove material you'll get stress relieving and dimensional distortion. Less in annealed or stress proof material but you'll still get some. The best approach is to rough all the dimensions first then do your finished passes to size after as much stress as possible has been relieved.

Greg

 

[Bob Korves]

The best material for a back plate is cast iron.

 

[JimDawson]

I guess you could rough it in, then throw it in your kitchen oven at about 350ºF for a couple of hours, then finish machining when cool. But I agree with Bob, cast iron is the preferred material for back plates. It's stable and vibration dampening to some degree.

 

[Chipper5783]

What is it about spindle adapter plates lately? fvd did not say what the application was for - perhaps mounting a chuck? There have been a few threads on this topic in the past month.

fvd - please keep us posted on your progress. I'm guessing the 4130 material was free and it is difficult to get the preferred material? Also, I assume simply buying a blank adapter plate is not easy in your location (or expensive to ship, or you need it right away??)?

I recently got a 5" D1-4 from Shars. I think it was $56US (it isn't very big, I was able to ship to a US address, so shipping was very reasonable). The fit to the spindle was good, and after about 15 minutes of tuning - the fit was perfect. The material cut nicely.

I'm with Daryl, I'll watch.

 

[4GSR]

4130 pre-hard or EN19 is already normalized, quenched & tempered to 28-36 HRC. You should not have any problem with it distorting on you. If you were using 41xx as rolled, you probably would have some distortion. I work with this material most of the time and the heat treated conditions are fairly distortion free until you start working with long shafts and sort.

One thing you want to remember, the harder the back plate material is, the greater chance it will damage your spindle over time. That is why you generally make back plates out of cast or ductile iron and not steel. Mild steel is fine such as 1018-1026 is fine. I will say, I'm guilty of it too! Ken

 

[fvdbergh]

^^ This is what the back plate looks like at the moment. The orange taper (seen through translucent body) is the 7.125 degree D1-4 taper, and should preferably be soft (going by Ken's advice).
The green taper is an arbitrary 8 degree taper (20 mm deep) for fitting the actual attachment of interest, another ER20 collet chuck:

(purple taper is for the ER20 collets).
I currently have a full set of precision ER20 collets, hence the comparatively small collet chuck. Building the chuck in two pieces gives me the option of bumping in the ER20 if needed, and I can later make an ER40 chuck if I really need it.

I guess that neither my 8 degree taper (green), nor the D1-4 taper (orange) really needs to be 30 HRC, but I would like the ER20 taper (purple) to be as hard as possible without having to grind it (no access to that type of grinding equipment).

Maybe I should use 4130 annealed (or cast iron) for the backplate, and 4130 pre-hard for the collet chuck only?

-Frans

 

[fvdbergh]

fvd - please keep us posted on your progress. I'm guessing the 4130 material was free and it is difficult to get the preferred material? Also, I assume simply buying a blank adapter plate is not easy in your location (or expensive to ship, or you need it right away??)?

I recently got a 5" D1-4 from Shars. I think it was $56US (it isn't very big, I was able to ship to a US address, so shipping was very reasonable).

Well, I would still have to buy the 4130, but I should be able to get cast iron too. I just prefer the way in which the 4130 machines.

Shipping is a significant problem. Our postal service is no good at the moment -- my last parcel from Hong Kong has been sitting at the distribution depot for the last 10 months. Using a courier for such a (relatively) large item is a bit pricey.

 

[joshua43214]

This is interesting to me.
I had just started to plan making an ER40 collet chuck for my lathe. After looking over the options for material, I settled on 1144 (Stressproof) as the right choice since I was not going to heat treat. After doing some further research, I came across some threads on PM that had folks getting over a decades worth out of 1018 in a light professional setting.
I suppose the moral of the story is that just about anything works provided it is not used all day every day.