Stainless steel bolt -- aluminum body. What could go wrong?

[cmonroe54]

The sheaves on my boom are obviously way passed expired, so...

I tried to remove the boom ends so I could access the sheaves, and they (the aluminum boom caps) were held in with stainless steel bolts. The last time I ran into this the 3/8” bolt had a hex head. This time it is maybe an 8-32 with a slotted head. Any sugjestion on how to get them out without drilling and re-tapping the cap or burning the paint of the boom?

Thanks.

 

[LeslieTroyer]

Hand held impact driver you hit with a hammer?? Lots of kroil.
https://www.homedepot.com/p/Powerbu...gclsrc=aw.ds&dclid=CM6Ti9ix3toCFQhpfgodCHEDyw
Les

 

[Charlie Jones s/v Tehani]

very common- get used to it I'd have said heat except for the paint stuff. Leslie has good suggestion

 

[dlochner]

Lots of PB Blaster, some time, impact driver, time, more PB Blaster.

 

[capta]

Chances are you are going to have to drill them out and move up a size on replacement. Not at all easy and it must be done slowly and very carefully. Do your best not to break the heads off as the resulting surface will make drilling much harder. Heat will work if you can heat the alloy more than the SS. I'm a real fan of PB Blaster, but it's more for steel applications.
I had a similar problem w/my Profurl RF on the headstay. My rigger replaced the SS with titanium, which apparently does not react as SS does to alloy, but this might be overkill for your application.

 

[JimInPB]

On average, aluminum has roughly 1/3 more expansion than stainless when heated. Extreme cooling, by soaking in dry ice for half an hour, followed by some gentle heat on the aluminum, may help the parts to give up their grip. I have used this trick with a wide variety of dissimilar metals that had become married to each other in various ways. I have used it to get fly wheels off of taper shafts on old outboards & I have used it to get a ruptured brass case out of an ordinance chamber. I have had very good luck with this method. This trick only works when the two metals have a significant difference in expansion rates. a 20% difference is often enough.

https://www.engineeringtoolbox.com/linear-expansion-coefficients-d_95.html

Soaking in vinegar first is sometimes also helpful. The acid seems to attack the metal oxides faster than it attacks the metals. Sometimes this loosens the grip.

 

[Rick486]

Is it possible to cut the entire cap off, remove the short piece of aluminum boom, and replace?

 

[Captain Larry-DH]

Chances are you are going to have to drill them out and move up a size on replacement. Not at all easy and it must be done slowly and very carefully. Do your best not to break the heads off as the resulting surface will make drilling much harder. Heat will work if you can heat the alloy more than the SS. I'm a real fan of PB Blaster, but it's more for steel applications.
I had a similar problem w/my Profurl RF on the headstay. My rigger replaced the SS with titanium, which apparently does not react as SS does to alloy, but this might be overkill for your application.

If heat/cold/impact/PB fails, I agree drilling is the last resort. Stainless is tough to drill, and you are “screwed“ if the bit wanders off to the side into the softer aluminum- so to assure you stay in the bolts center; start with a new (sharp) 1/16th bit and use a drop of oil with steady pressure on slow speed to aid cutting. Follow with successively larger diameter bits.

PS - I once had a an “easy out” bit break inside a stainless bolt I was trying to get out. Then I was faced with a hardened tool steel core inside stainless bolt inside softer aluminum! I eventually ground it all out using up several Dremel chain saw sharpening bits.

 

[sailnoproblem]

I agree with Les. First spray with PB Blaster. If that fails and you have to drill the stainless out, I would try to start with a Center Drill, then continue with a HSS Drill Bit. The Center Drill has less tendency to walk.

 

[LeslieTroyer]

If I have to drill out a machine screw/bolt I use reverse twist drill bits. It is surprising how many times the screw will just spin out after just a little bit.

Les

 

[allanb]

I have used the following to precisely drill out rivets without hogging out the holes. Could work well on seized screws if the right size can be selected.

Rockler Insty-Drive Self-Centering Bits

 

[cmonroe54]

Thank you to all who commented here. You said pretty much what I thought I'd hear, though I like the reverse twist drill bit comment. I'll remember the Rockler Insty-Drive Self-Centering Bits.

 

[Rich Stidger]

I will add- Rather than a hand impact tool, for fasteners the size you are working on, I have had decent luck with an 18V impact driver. I have a Ryobi but there are others as well. The key is to soak with PB Blaster for a couple days and be very careful not to let the slotted bit slip in the screw. The hand-held light weight combined with variable speed and torque that is not excessive is a real plus.

 

[Jacktar]

build a clay dam around it and fill with standard carbonated soda any brand. Let sit for hour or two, repeat then try with proper sized screwdriver.

 

[rgranger]

Extreme cooling, by soaking in dry ice for half an hour, followed by some gentle heat on the aluminum, may help the parts to give up their grip.

Ooooh.... I like that! I think I'll have to go out to the shed and look for a stuck bolt. I have access to liquid nitrogen but that might be getting carried-er (new word) away.
I'll definitely keep that one in the bank and hope to pull it out some day.

 

[rgranger]

build a clay dam around it and fill with standard carbonated soda any brand. Let sit for hour or two, repeat then try with proper sized screwdriver.

That is actually not a bad idea. Chemically it is similar to the suggestion above to use vinegar. Both are dilute acids.

 

[rpwillia]

I vote with Leslie's 2nd suggestion and Rich impact drive on this. I expect the impact driver Leslie first mentioned would cause a dent as you have to hit them pretty hard and the aluminum on your boom is not all that thick.

 

[allanb]

This is the actual tool I have used to rill out blind rivets of various sizes. Could be used to center a drill bit on a screw head. Aircraft tool supply catalogs tend to cause me to open my wallet