Please - I need help drilling holes

[Derek122]

I am trying to drill holes in a RC60 chrome alloy material. The challenge is that a 3/8" hole exisits already, and when I try to drill a 5/8" hole, we get lots of vibration. The part is not flat, which makes it more difficult. Any ideas please of a drill bit you think will drill such a meterial?

Thanks

Derek

 

[saberblue]

Depending on how many you have to do there are several approaches the come to mind:
1- mount the part on the head stock of a manual lathe and set it up with the hole properly located and then using either a set of reamers and cut the hole larger with each progressively larger reamers -- typically 0.015" per reamer you will need a very heavy duty oil to reduce cutting forces and reduce vibrations
2- set up as above and then use a core drill -- these are drills specifically designed to increase the diameter of a pre drilled hole
3-EDM the hole using either a wire or sinker EDM

many of these decisions will be based on how ridged and how much power you have available on the machines you will be using -- my thought about the manual lathe is that almost every shop has on back in the corner and if you have some one who can still run it the set up should be pretty straight forward.

Good luck and happy drilling

 

[Compositepro]

A step drill may work in a drill press.

Mount the work rigidly in a milling machine and create the hole with an end-mill.

 

[MikeHalloran]

Clamp the part in a drill press with the hole axis vertical.
Plug the 3/8" hole with, e.g., putty.
Build a dam around the outside of where the 5/8" hole will go, with, e.g., putty.
Fill the dam with grinding compound, diluted a little if necessary.
Chuck a piece of 5/8" copper tube.
Press the tube into the grit pool to charge it,
then start the spindle turning slowly, and feed the tube down until it stops cutting.
Repeat the charging and lapping until the tube breaks through.



Mike Halloran
Pembroke Pines, FL, USA

 

[Derek122]

Thanks for all the responses. The Step-Bit sounds like the way I want to try first. Do you have a link for such a bit? Thanks

 

[Compositepro]

http://www.irwin.com/tools/drill-bits/unibit-step-drill-sets

 

[arunmrao]

Derek,

why did you choose to drill the hole in the hardened condition. You could have done it in annealed condition along with your other operations,finally heat treated and finish machined.

This is quite a challenge,ensure the job is rigidly clamped,the tool holder is heavy and the machine bed is capable of absorbing the vibrations,else broken drill bit will be another challenge.

Good Luck !

_____________________________________
"It's better to die standing than live your whole life on the knees" by Peter Mayle in his book A Good Year

 

[unclesyd]

If possible I would jig grind the hole to size. To drill to size I would use a drill bit for hardened steel from B A Manufacturing.
As posted above a rigided setup is required,

http://www.bamanufacturing.com/sp_series.html

MikeHolloran,
You are betraying your age. The only thing you missed is to use turpentine as a lubricant.

 

[MikeHalloran]

I like those weird drill bits for hardened steel, too, but:
- I'm not sure they'd like working in a predrilled hole.
- They're fairly expensive.
- You need a lot of spindle HP at the size requested.
- Since they work by rubbing/burning/melting the workpiece, you get a sizable blued HAZ, which may not be desirable.



I'm okay with my age. In my journey toward eventual decrepitude, I've learned a fair number of right ways to do things, mostly by doing them wrong in a much larger number of ways.



Mike Halloran
Pembroke Pines, FL, USA

 

[racookpe1978]

Try a four-flute drill, rather than a standard 2-sided bit.

get a hollow drill (like a Houghen or 5/8 dia Milwaukee part number 49-59-0625 with a pilot bit in the tip). These cut from the surface straight down, rather than from a pilot hole outward from a 119 degree sloped tip.

As the others point out, clamp your work firmly, aim the bit with the pilot tip of the bit and adjust for center with the drill press.

 

[ornerynorsk]

What is the thickness of the material and how many holes do you have to do?

Anything HSS is going to be absolutely useless in that hard of material. Carbide will be only marginally better.

You might try single point boring with a good quality carbide bar, or a carbide endmill as compositepro has suggested.



It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[NickE]

I'd go sinker edm, or mike's copper pipe/grinding cpd.

Mike-would coarse diamond lapping compound work?

Nick
I love science!

 

[MikeHalloran]

Diamond would work, but so would valve grinding compound, which is cheaper for most of us.



Mike Halloran
Pembroke Pines, FL, USA

 

[BenWhite]

sounds like your going to need carbide. If you have time, and money, or if this is a really important piece/hole, then you could get it water jeted. These guys do low production runs

http://www.leadingedgefab.com/

often profiling, and drilling blanks for individual knife makers. It may be expensive for just one piece, but it is guarantied to give you a perfect hole

 

[maulidinbastian]

THere are the options:
1. Use EDM
2. Drilling and use anvil to hold Drilled part then make annealing to put the mech properties back to initial