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"http://www.youtube.com/watch?v=QpYFTQCsSGI"]YouTube - How to tap hardened steel video from Guhring
http://www.guhring.com/documents/cat...TapCatalog.pdf
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Hello all,
I found my way here in hopes of getting some help with a project. I'm building a custom center differential for a radio controlled monster truck.
One of the pieces of the diff needs two M3x0.5 holes drilled and tapped into a hardened steel cap (see pics). I brought the piece to a machine shop, they said it would be no problem. Then they called back a day later and said it was too hard and they weren't even able to make a dent in it. This was hard for me to believe. I think they decided it was going to be more work than the $30 they quoted me and just said forget it.
So now I'm stuck trying to do it myself. I ordered a couple different cobalt bits and one full-carbide bit and a cobalt tap. This was at the advice of a couple members of the RC forum I frequent.
What I'm wondering is if anyone can give any tips on how to do the drilling/tapping? Is there any way I can soften the hardened steel by heating it?
I've already put a good amount of time and money into this project so I don't want to give up without knowing I've tried everything. Thanks for any help in advance!
(The hardened steel cap is sandwiched in between the plastic spur gear and the plastic diff cup. I will post better pics of the cap by itself if that will help)
"http://www.youtube.com/watch?v=QpYFTQCsSGI"]YouTube - How to tap hardened steel video from Guhring
http://www.guhring.com/documents/cat...TapCatalog.pdf
Patience and perseverance have a magical effect before which difficulties disappear and obstacles vanish.
Thanks for the reply. Wish I had a machine that could do that for me!
The only tools I have are a drill press and hand taps. I thought the best idea was to let a machine shop do the work because they have the proper machines and tools. Yet they tell me they couldn't drill into the steel? I think they are BSing me, but now I have no choice but to do it myself.
I'm looking for input on things like do I need to use some type of cutting fluid? Should I use the cobalt bits or carbide? Any general tips on drilling/tapping hardened steel would be helpful.
No I would'nt use cobalt. anneal the spot with a propane torch try marking the spot with a center punch to keep track of where you are.keep the inner blue flame tip ( the prettiest cone)on that spot for about ten minutes if the spot on the metal starts to change colors like to a dull red that enough, and then let it cool to the point where you can touch it bare handed, then use a brand new high speed steel drill bit. Make sure to lubricate very well and keep alot of pressure on it and go slow, always removing chips and spraying with wd40. All methods are with a drill press, use vice or clamp down. Or you could use a self annealing bit or diamond bit, same with these though high pressure and with all methods also "peck" going in and out to cool and lubricate and clear chips. Hope that helpsOriginally Posted by simplechamp
Welcome to the forum.
Tell us more about this hardened cap.
Why is it hardened?
What purpose does it serve?
How many of these do you have to do?
Any idea what kind of metal it is?
Where did you get it?
Reason I'm asking is that unknown metal of unknown hardness (also known as mystery metal) can give you fits of rage. Perhaps the best way to approach this is to get the caps made from known quantities. If it has to be THAT hard, get a hardening steel.
I understand you don't have much in the way of tooling and I admire you trying to do it yourself. But broken bits or worse, taps, and money spent can be a real downer.
If you are prototyping and need someone to help with the machining, post an RFQ here, there are several people, myself included, who love to help out with these kind of things.
Regards,
MM
859-421-6233
The cap is actually a modified spur gear from a different RC truck differential. As a gear it needed to be hardened because the pinion/spur contact would cause too much wear on any softer materials.
The way it's being used now, modified with the teeth ground off, it doesn't need to be hardened at all. I would prefer a much softer material actually. The problem is I am going off of someone elses design and that's what has to be used (unless you made the piece from scratch). To have a single cap made from scratch would be prohibitively expensive so I'm stuck modifying the hardened spur. I looked at using other RC truck spurs but they are all made of hardened steel.
I am only making one of these for personal use on my truck. I will try to soften it with spot annealling and see if that helps. I'm in contact with other people who have drilled/tapped this cap before and they say it can be done, but it's just a pain in the butt to do so.
Video shows 42CrMo4 which is equal to 4140 and can be tapped.
Since they were not able to dent it (I assume with a ball peen hammer) it is most likely made from a alloy steel and hardened throughout. You will not be able to tap it. It has to be annealed and re-hardened. Not recommended since you don't know what steel it is made from.
Try again to use a ball peen hammer on an area that is not critical. If you get a dent - use a carbide drill to break thru the case. It must be larger than 3mm. Than drill 2.5mm and tap.
I don't give much creedance to the guys at the machine shop saying the couldn't drill it. I have been in contact with the guys who have done this project before, and it can be done. It's just a tough job. But they all did it on a home drill press too
I have a carbide bit (2.5mm) and cobalt bits (size #40) and also some diamond and carbide dremel bits to "break the hard shell" like you mentioned and others mentioned on the RC forum I frequent. I also have some cutting fluid/lubricant. I plan on spot annealing the places where the piece needs to be drilled.
Well, I'm off to go see what I can do, wish me luck! If I fail I might be putting in a job request for one of you guys with better equipment and more experience!
Well everything went very well and I got the holes drilled and tapped.
I annealed the metal, used a diamond tip bur to make a divot, drilled with the carbide bit, and tapped with the cobalt tap. It was actually WAY easier than I expected. Do you think the annealing really helped that much? Or just using the right tools for the job made it easier? Or both?
Thanks to everyone for your helpful input. I'll be sticking around to learn as much as possible because I have plenty of projects for my RC cars in the works and I need to build my skills and learn more. I am about to graduate with my associate in automation tech. and I have a good handle on theory and programming but not so much with mechanical and hands-on work.
Do you guys build your own little CNC mills? I think that would be very neat to do, and it would be great to have a little mill for my RC projects. Could you build a simple mill out of a couple servo drives and a controller and some t-slot profiles? During my internship this summer I did design work with 80/20 and I just love that stuff!
Heat treatment (or the ability to heat treat) pretty much differentiates mild joe steel from the stuff that goes into knife blades or drillbits.
http://www.matweb.com/search/DataShe...88f63c6500d36b
http://www.matweb.com/search/DataShe...b1a46a1f1eb1c3
Those links point to a relatively common heat treatable steel alloy. It's not an extremely hard one, but it's one that goes from a nice machinable Rc13 to a pretty hard Rc55. It's hard to immediately appreciate those numbers, but for a bit of rough reference, Rc13 is about in the range of a soft steel nail. You can file it and most steels in that hardness range (save cast steel) tend to be pretty ductile. You can bend it or swage it to various deformed shape. Rc55 is very hard. It's a decent hardness for making a knife that can be honed to a razor sharp hair splitting edge. 55Rc is about the lower end of hardness range for a decent drill bit. Most Rc55 steels are brittle and don't do much plastic deformation before breaking.
Annealing hard tempered 4140 would take it out of the drill bit range hardness and put it's hardness somewhere in the range of mild steel which is easy to drill.
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