Hello all,
I have a welding service in Phoenix and regularly am called out to repair aluminum trannies and engine blocks. To date I have had no problem repairing these as they are pretty straight forward. However, this last call yesterday was everything but.
I was called out to repair some broken motor mounting points on what turned out to be a cast iron block. I was not prepared for this repair as I only carry about a half a dozen ni-rods and this one would have taken at least a dozen and maybe two dozen. This was basically a build up job of filling in the broken threaded holes (there were two broken mounting holes) and putting enough material down to drill a fresh hole and tap it.
I made the decision to with brazing rod and flux as the fact that I was brazing on the outside of the block (where it meets the tranny) meant that expansion would go outwards without running into obstructions (like gussets, etc.) that may build up stresses when it expanded and cooled. In short, the metal was free to expand as much as it wanted in any direction and shrink again without running into stress points.
I tinned the surface and brazed away, building up both mounting lugs with enough material for the next step. The bronze bonded great in textbook fashion. Keep in mind that I have never attempted this type of repair in this fashion before.
Once cooled, I marked off the excess material to be cut off using the engine mount as my template. I marked the holes in this fashion with a sharpie, center punched them and drilled out the holes. So far so good, everything was going beyond my wildest dreams.
Now the *****!! When I attempted to cut threads into the holes I found that the brass was too brittle and I was unable to continue with the plan. Every time the tap cut into the brass and grabbed, the next twist broke the beginning threads and the tap stopped cutting. After a few efforts, it was evident I needed to stop and assess where I was at. Unless there is something that will make cutting the threads possible, I think I have to abandon the "cutting threads" route. I am hand cutting the threads with tap and hand "T" chuck.
What are my options? I have thought of only two.
1.) To drill out the hole and sink a stud in it to be held with an industrial epoxy like JB weld. I picked some stuff up at the local welding supply that's called "Lab Metal" which is sold not as an adhesive, but as a filler material. Among its list describing uses is "repair of over-bored holes". This is exactly what I had in mind. Over-boring the hole, sinking the stud in it and filling it with this stuff that would grab the threads and fill into recesses that I would cut into the hole with a high speed burr.
2.) See if a silver solder could be employed to solder the stud into the hole. I could over-bore the hole slightly larger than the stud, enough to be a slip fit, heat the area and let the solder get sucked into the hole via capillary action, forming a tight bond and mechanically sound (hopefully) joint that would stand up to the abuse engine mounts take on a daily basis.
Anyone have any thoughts on this one? My first choice would be to try and cut the threads, but am not sure how to go about it given my experience so far.
Any and all ideas will be considered seriously.
Thanks in advance,
Tony
Tony,
First off, Phoenix. I'm in Prescott area. Hello neighbor.
Second, could be your cutting fluid. Don't use just a drill and saw coolant. Try Rapid Tap tapping fluids. Make sure it says it does several of the alloys for brass, bronze, copper, etc. I also keep one specifically for alum, 'Alumicut' I believe. You may have better luck with the right fluid for your material in order to tap successfully. If you are already using a good tapping fluid, Plan 'B';
But, I'm not sure of your plan B's. Is there room to just use all thread and put a nut on BOTH sides without the threaded holes or the epoxy? I'm afraid your other ideas will just pull out with very much force applied. Don't know this for sure, just my first impression. I have never repaired one that way. Not with bronze either. I have always built one like that up with Ni rod.
Sorry I wasn't able to be of more help.
Have a Great Day, Brent
Hi Brent,
thanks for the reply and suggestion. I think the problem may be coming from the fact that I am doing it by hand and can't help but move off center a bit while turning the tap. On steel this is not a problem as the metal is malleable enough to absorb the movement without breaking the barely cut thread and finally will self center the tap once several threads have been cut. Since I am threading on a horizontal surface and there is obstructions near the built up area so I can't get a full twist with the tap, I have to do 1/2 turns, let up and another 1/2 turn.
I was thinking maybe I need to use a drill on slow speed and apply pressure. What do you think? How about the silver solder approach. Have you ever tried this stuff. I have, it is very strong. Bikes are silver soldered in fact, also brazed. I have never used it in this type of setting though.
Regarding the cutting fluid, I will pick some up today as I ran out and was using WD-40 which on steel worked ok. I think I used "Rapid-tap".
Thanks "neighbor",
Tony
Tony,
The drill approach would more than likely be a better avenue than the T handle in this situation. Not sure it will 'solve' the problem. But combined with proper cutting fluid it may do the trick.
Never used Silver solder in the fashion you are wanting info on so hopefully some of the other guys can fix you up with the info you need.
Have a Great Day, Brent
Hi Brent,
I am going to return in a few minutes to continue the project. I am going armed with a tapered tap this time as I think that it will better my chances of getting the threads started. I have been using a tap with a slight camber to try and cut the threads, but realized after doing a little research that the tapered ones are recommended when there is difficulty cutting threads as they will begin cutting slightly at first and then deeper as you screw in.
I will also get fluid that explicitly says for brass, bronze, etc.
If push comes to shove, I will braze a stud into the hole after drilling it out so it slips in. Instead of a bolt to attach the mount, it will have a permanent stud.
Thanks,
Tony
Tony,
Sounds like a sound procedure. Hope it all works out.
Have a Great Day, Brent
Try the Allstate or Bernz o Matic " Nickel Silver " a nickek bearing brazing rod -
I brazed a vise back in 1966 and it is still working today - dynamite stuff -
Hi Cobra,
thanks for the feedback. Will this silver solder or brazing rod "flow" into the joint? I prefer that route over the industrial adhesive approach simply because it is a metallurgical bond as opposed to a pure chemical bond.
I will see if Allstate can suggest a material for this application. Good idea.
Thanks,
Tony
The taper tap & proper cutting fluid should help a lot.
If You end up silver soldering the stud, just be sure that the silver solder flows at a temperature below the brazing rod You used. If You get a proper "sweat" joint the silver solder should be strong enough. Use a bolt with the head cut off, You want only a few thousanths gap for a good joint.
Hello Dave and all,
I was able to make the threads finally using a new tapered tap. The one I was using was more of a thread chasing tap and so did not allow me to start the threads properly since I could not hold it absolutely still nor in line 100%. The tapered one went in like butter and grabbed after a few twists, practically self-centered itself and also the application of a cutting oil called "Sprayon".
My plan "B" would have been to braze the stud in place after having countersunk the hole with a countersinking bit. This would have allowed me to braze it in place and have a relatively flat surface when done.
I want to thank all who gave me their advice and opinions. A few were new to me and others reinforced my approach. For example on aother forum one advice was to use the silver solder bolstered my feeling that it is a good, strong material. The member said that he personally had performed destructive testing on silver soldered joints and found that the base metal broke before the soldered joint did. This was my gut feeling to.
In fact I called "Allstate" today (which is a division of ESAB now) to ask about the strength of their silver solder (no. 155) and the feasibility of using it the way I had planned. He said he didn't think it was strong enough because it was "ONLY rated at 55,000 psi. I told him, WHAT? That's damn near the strength of 6010 rod, what do you mean its not strong enough? I had visions of all the things I have welded in my lifetime with 6010 and said to myself "THAT'S THE STUFF TO USE". I didn't mean to embarrass him and hope I didn't. He finally suggested that I simply braze the studs in the block. I think he was right too and that became my plan "B". No need to have to buy the silver solder with plenty of bronze on hand. I thanked him for his help and filed away in my brain this procedure and to put getting some no. 155 to have on hand on my truck as I never know when it may come in handy.
Another idea that was offered to me was to use regular 7018 to build up the engine block instead of ni-rod or bronze. The member suggested that I burn 1/2 of a rod and peen it until cool and then another and so on until it was built up. This was to preserve the color match and provide similar metallurgical composition. I would have never thought of doing that as it is so "non-standard", but according to him, that's what works for repairs he has done to cast iron. It was from the www.smokestak.com forum, made up of people who restore antique tractors and related stuff. I have to respect their opinions on the subject as they deal with this stuff all the time so his opinion carried credibility with it.
Thanks again to all. This thread is officially over and solved. I will try to post some pictures of the finished job.
Tony
If You would have used the 7018 rod the steel deposit would have too much carbon where the steel & cast iron intermix and that are would be brittle and non machinable.
The nickel silver rod someone else mentioned is even stronger than normal brazing rod, If I remember 80,000 tensil or above.
The block is probably only 40,000 tensil, maybe more maybe less.
Brazing alloys generally excede the yield point of mild steel, something not everybody understands.
Hi Dave,
thanks for the information. I get amazed at how unlimited the breadth of knowledge that we continue to pickup throughout our lives. I have been at this trade for over 30 years. When I was most challenged was as a maintenance welder back in Chicago Steel mills years ago. I was hit with every possible combination of metal working repair problem conceivable.
The old timers passed on their tricks to the new guys and the new guys sifted through the stuff the old timers "taught" them. I learned the hard way that just because someone has been doing something for a long time doesn't necessarily mean they were doing it the right way. On the other hand, we new guys learned that the old timers are "old-timers" for a reason and those reasons could mean the difference of whether we left the job in our car or in a body bag, especially in a steel mill environment.
In all that time I don't think I ever had to drill and tap bronze / brass so it took me by surprise when I couldn't do it the first time as I reported because I knew at its basic level, it was not different than the dozens of holes that I've had to drill and tap after building up material in similar situations. Just that it was not brass.
I have enough experience under my belt to know that there is always plan "B" or "C", etc. But of course I preferred plan "A" (cut the threads). Now this is permanently etched in my brain and I will not run into this problem a second time (knock on wood!). Maybe a variation of it, but not this same one.
Thanks everyone for helping me learn.
Tony
A bit more information on the taps:
Hand taps often come as a set of 3 in a box, taper, plug & bottom. The taper tap is the easyest one to use, and in a through hole, the only one You need. The plug tap has a shorter lead in, and the bottom tap has the shortest. These are used where the threads need to go as deep as possible in a blind hole. Use them in order, but be carefull about jaming the end of the tap in the bottom of the hole. When You get to the bottom STOP!!! These taps are intended to be backed up periodicly to break the chips when used in ductile materials.
Spiral point or "gun" taps work best in deep holes or through holes. The tap is ground to send the chips in front of the tap, and should not be reversed to break chips. These are commonly used in power driven machine tapping aplications, but cann be used by hand as well.
Spiral flute taps have spiral flutes like a twist drill, the chips come up the flute like with a drill bit. These are generally used in machine operation, but they too would work by hand.
Hello Tony, I haven't contributed to your thread, but I have followed it. Your most recent post serves to press home some of the basic ideas of a career and life in general, you're never done learning unless you allow yourself to be. This thread and so many others that forum members have contributed to and participated in goes to show that we will always face challenges that are new to us and even in today's somewhat cynical world there are plenty of folks who are willing to help one another out. Have enjoyed reading of your challenge here and the responses of others, look forward to your contributions in future posts and topics. Best regards, Allan
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