Questions for experienced metal workers or engineers

fast14riot

fast14riot

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Oct 27, 2010
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Ok guys, here is the problem, I have a blind hole that needs to be filled. Base material is 4140 heat treated, and unable to be re-heat treated so welding is out. Hole is ~0.375" x 0.625" oval shaped and square to the face. It needs to be rust blued for protection, and cosmetically I would like it to match the base metal once blued. I was thinking of taking a piece that is cut to fit, and peen the edges over to hold it in place. I would leave it maybe .010 proud before peening and dress it flush with a file. My issue is this "plug" may need to be D&T'ed down the road, so it is possible to peen the edges of heat treated 4140? Should I leave it in a soft/semi soft state or will this not be strong enough to hold threads well? Oh yeah, I almost forgot, it will be subjected to shock loads in the range of 57 to 60 Kpsi. Will this type of mechanical attachment be able to survive loads like this?

I have been doing tons of research on this and am getting confused. My training is in metrology, not engineering, PLEASE HELP!!!


Thanx in advance-
-Xander
 
You could do a shrink fit. Warm the base piece up to the temperature it was tempered at and measure. Then use dry ice to cool an oversize plug and measure it. Take the plug down enough so that it is a slight press fit cold while the base is hot. Heat treat the plug. Then cool in on dry ice and press it in. This might not work if there are any very thin walls on the sides of the hole. But, if you can do this the plug will be in there solid. TwinDisk is a big name transmission for very high powered diesels in boat applications. They shrink their gears onto the shafts with no keyways.
 
If you have the capabilities you can still weld after heat treat, we do this quite often on 4140. Preheat the block to around 500 or 600 degrees and using 4140 rod or mig wire you can weld the hole. place back in the hot oven and let it soak for a while then turn oven off and let stand or cool submerged in sand.
 
I would use soft 4140 as the plug, put a slight countersink on both sides of the heat treated part, cut your plug a bit thicker than the heat treated part and peen until you cant see the countersink grind flush.

Richard
 
ib2v4u said:
You could do a shrink fit. Warm the base piece up to the temperature it was tempered at and measure. Then use dry ice to cool an oversize plug and measure it. Take the plug down enough so that it is a slight press fit cold while the base is hot. Heat treat the plug. Then cool in on dry ice and press it in. This might not work if there are any very thin walls on the sides of the hole. But, if you can do this the plug will be in there solid. TwinDisk is a big name transmission for very high powered diesels in boat applications. They shrink their gears onto the shafts with no keyways.
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That's a very good idea. I may try and find an oven I can fit it into or a localizing heat source. There are not any thin walls in this structure, so this may actually work. It isn't subjected to any high heat so a cryo fit peice would be permanent. I'll have to dig up the heat treat data for these parts, but they were made a looonnng time ago, so wish me the best of luck!

chrisber said:
If you have the capabilities you can still weld after heat treat, we do this quite often on 4140. Preheat the block to around 500 or 600 degrees and using 4140 rod or mig wire you can weld the hole. place back in the hot oven and let it soak for a while then turn oven off and let stand or cool submerged in sand.
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I know it can be welded after HT, but in my case I don't want to loose the HT in the localized zone. I know that it should be welded with as little amperage as can hold an arc, but this is beyond my capabilities and the people I have spoken to expressed some conerns with doing it. I am not going to make someone who isn't comfortable doing it, do it anyways.

Tinbasher said:
I would use soft 4140 as the plug, put a slight countersink on both sides of the heat treated part, cut your plug a bit thicker than the heat treated part and peen until you cant see the countersink grind flush.

Richard
Click to expand...

That is what I was planning to do, but being a blind hole I am going to have to cut/grind a small recess into the side wall just below the face of the hole. This shold keep it from pushing it out with the shock from 60,000 psi.


What does everyone think about soft 4140 holding threads? If it is D&T any load will be shared with a bridge and one other hole in the base material, another bridge then to another double secured footing in the base material. A double cascade, if you will.


Thanx
-Xander
 
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Ask your gunsmith

I'm thinking tapered pin, but the welding sounds good if you know who to take it to.
 
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No Idea how big your piece is, but you could set it in sand piled on a piece of plate setting on several hot plates and warm it up pretty even. Might need to add a little localized heat in the plug area checking with a temp crayon. Just 350-400f will get you a bit, not affect the temper and the -100 will shrink the plug well. Have both pieces really clean and have a slight taper on the bottom of the plug so it starts easy. Then hold it in place with tongs and give it a solid wack with a brass hammer.
 
fast14riot said:
That's a very good idea. I may try and find an oven I can fit it into or a localizing heat source. There are not any thin walls in this structure, so this may actually work. It isn't subjected to any high heat so a cryo fit peice would be permanent. I'll have to dig up the heat treat data for these parts, but they were made a looonnng time ago, so wish me the best of luck!
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I know a guy around here that can most likely weld it up for you. He is in Hayward. I've had him weld up some hardened dies for me. He welded and peened the area, and it held up very well.

Let me know if you want to go this route, and I'll see if I can dig up his info.

A picture tells a thousand words. If you post one it may help.
 
Can you drill and tap the hole for a bolt made out of 4140 and have the top of it welded to fill in the gap.

What is the application?
 
12345678910 said:
Ask your gunsmith...
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ugh, last time I spoke to him he lectured me about how GTAW aka TIG welding isn't going to work, it can only be heliarc'd. I don't trust him to weld for me anymore...

Carl_First_Timer said:
I know a guy around here... Let me know if you want to go this route, and I'll see if I can dig up his info.

A picture tells a thousand words. If you post one it may help.
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Carl, thanx. I may be in touch with you. I have a long day today, 16 hours, so if I am still standing and functioning when I get home I may be able to get a picture.

Zanderman said:
Can you drill and tap the hole for a bolt ...
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not really, it is an oblong recess. 3/8 x 5/8. Like you took and end mill and made a short pass.


Thanks for the help guys, Feel free to put out any more ideas you may have.


-Xander
 
fast14riot said:
ugh, last time I spoke to him he lectured me about how GTAW aka TIG welding isn't going to work, it can only be heliarc'd. I don't trust him to weld for me anymore...


-Xander
Click to expand...


Ya, I should have said a GOOD gunsmith.

I expected that most of them would ship it out to a specialized welder & He would know that 1 good welder in your area.
 
I would do what Zander recommends and drill/tap and then red loctite and peen the bolt in the threads then grind flush. Works for me, although it might be tricky to tap hardened steel, it is still doable.
Chris
 
12345678910 said:
Ya, I should have said a GOOD gunsmith.

I expected that most of them would ship it out to a specialized welder & He would know that 1 good welder in your area.
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Yeah I getchya. He is darn good mechanically, and has done many jobs for me over the years but is horribly slow. I forgot he had a gun of mine once, until the bill showed up.

I have spoken with several local people about this particular project, including x-ray certified welders and they expressed some concern but it is do-able. So far I like the idea of a cryo fit, but am open to talking to some specialized welders who can do T&D type work.


-Xander
 
There is also ultrasonic welding, depending on how much you want to spend. I know a place in Fremont that does that.

EDIT: oh and btw there are size limitations to that. :(
 
Ok thanx Mete. I was wondering if it should be HT'd or not. I don't have my books in front of me, does anyone have the HT info for 4140 and the CTE? I guess it would fall under the thin sections data as it is only about .5" thick.


-Xander
 
Without pictures or knowing what the part is this is all speculation...but...

Is this hole an original feature of the piece that needs to be filled for cosmetic or other reasons? Or is it an "oops"? If it's an oops and on a mission critical part, the failure of which could cause death or injury... scrap it. For a piece subjected to shock loading, any hole, unless fixed by very very good welding, can and will act as a stress riser causing the piece to fail. Even a good weld can still act as a stress riser.

I'm guessing from your original post that this hole is the result of something unfortunate happening to a threaded hole in the part, hence the possible future drilling and tapping. One option would be milling out the hole to a larger round size, threading it, and putting a threaded insert in with a hole having the desired threads in the center. But making the hole larger could make the part too weak, if the OEM or a PE can't certify that it will still be strong enough.....

If filling the hole is for cosmetic reasons only, and you are rust bluing for corrosion protection, consider that the tiny gap between your peened or press fit plug and the piece is an invitation for corrosion to enter and begin working unseen around and below your plug. No matter how well fit your plug is, there will still be enough of a gap...Murphy says so.. Soldering or brazing the plug in place could solve that problem, at the risk of galvanic corrosion...and a visible ring around the plug. Threads and pipe sealant might be a good choice. If you could use a coating for rust protection, you could fill the hole with some form of epoxy or low temperature alloy that would seal well to the steel, and they say JB Weld can be tapped...

The more details about the piece that you can share, the more likely it is someone will come up with useful advice
 
Mahoney said:
Without pictures or knowing what the part is this is all speculation...but...

Is this hole an original feature of the piece that needs to be filled for cosmetic or other reasons? Or is it an "oops"? If it's an oops and on a mission critical part, the failure of which could cause death or injury... scrap it. For a piece subjected to shock loading, any hole, unless fixed by very very good welding, can and will act as a stress riser causing the piece to fail. Even a good weld can still act as a stress riser.

I'm guessing from your original post that this hole is the result of something unfortunate happening to a threaded hole in the part, hence the possible future drilling and tapping. One option would be milling out the hole to a larger round size, threading it, and putting a threaded insert in with a hole having the desired threads in the center. But making the hole larger could make the part too weak, if the OEM or a PE can't certify that it will still be strong enough.....

If filling the hole is for cosmetic reasons only, and you are rust bluing for corrosion protection, consider that the tiny gap between your peened or press fit plug and the piece is an invitation for corrosion to enter and begin working unseen around and below your plug. No matter how well fit your plug is, there will still be enough of a gap...Murphy says so.. Soldering or brazing the plug in place could solve that problem, at the risk of galvanic corrosion...and a visible ring around the plug. Threads and pipe sealant might be a good choice. If you could use a coating for rust protection, you could fill the hole with some form of epoxy or low temperature alloy that would seal well to the steel, and they say JB Weld can be tapped...

The more details about the piece that you can share, the more likely it is someone will come up with useful advice
Click to expand...


The hole is an original feature, and is safe to withstand pessures up to 65kpsi with a large safety margin still. It is neeeding to be filled mostly for cosmetic reasons, and to provide a flat surface for an additional part that will overlap part of the recess. The D&T that would need to be done would be only of either 6-48 or 8-40, so it is a small hole compared to the piece filling the hole in question.

Good points you bring up on the cosmetics of filling the hole, I am aware of a tiny gap from cryo fitting a piece, more likely from a less than perfectly fit plug. It will have a constant coat of water displacing oil on it at all times. Ill try to get some pictures up in the next few hours.


-Xander
 
There is a purpleas well as a green loctite 672 or some number that is a sleeve retainer that will fill a .007 gap between mating parts. You will not move the piece after unless heat is applied. Very strong bond.
 
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