Suitable Drill Bit Grade For Making 8H7 Hole

Have you considered getting them laser or water cut?

No ..i cant..

I have to drill it "on assembly" after checking with CMM

You're unwilling to consider changing the process.

Just what advice do you expect us to give you?

Lol...

I am saying it is not possible... The guide pin comes in Rudder assembly jig and the part has to be checked in the jig with CMM. If i take the part out, on assembly dimension can't be achieved!! .. Thats the reason

Okay, so no change in process.

Slow the rotational speed of the drill, use plenty of lube, purchase lots of drills.

Or, will you tell us it is not possible to change drill rotation and feed rates.

are these pins harden through or just case hardened?

Do you have a way to keep the bits cool when drilling and to remove the drilled material?

Are you starting the holes with small diameter bits and then stepping up with intermediate and final diameter bits?

Phoenix .. The pins are through hardened

Usbport... We start with Dia 4 pilot hole then 5,6,7.8, and 8H7 Reamer. The drill bits and reamer are dipped in oil for lubrication / cooling .The holes are drilled with Pneumatic hand gun (Chicago Pneumatic)

Calculate your chip load,.......... chips can carry away a good part of the heat.....

May be hard with a manual drill....... but create a reference point and you can get you RPM squared.

But with what information the OP supplied........ it's not going to be easy.

Try using a proper metal cutting fluid for a start. And as lyn said hand drilling is never going to be very good. Can a custom made drill press (it can even use your current air drill) be made particularly for this job to ensure the drill is held as rigidly as possible at the correct angle, height, etc, etc?
Oil does lubricate but not very well, the main thing you have to do is remove heat from the cutting area. To do this you really need a water soluble oil based cutting fluid.

We used to make equipment, and one part was a hanging steel ball, where we had to drill through to attach a cable to. Lots of cooling, slow revolutions, but our best option to save on drill bits was to use a drill bit with widia (hard soldered ends) like used to drill in concrete. Of course a concrete drill bit does not have the right angles, but if you are handy with a grinder, you can make it work. One modified bit beat 20 pieces of HSS. Used diameter was 4mm. The ball was a big 40mm ball bearing ball.

Perhaps these bits are commercialized too, but we modified concrete drill bits.

Time for one hole on automatic drill press approx, 7 minutes. Re sharpening of bit: every 2 balls. Use of bits: 1 per 22 balls. Revs: 320 /min.

I read you do it with a hand drill.

You need to be patient, and when your drill is too fast, pulse the on/off knob, but keep pressure on the bit. Even with coolant you need to hear a creeping sound when drilling. (like drilling porcelain or glass)

Good luck

Sounds to me if our main problem is actually stability, if you construct a removable steel jig which allows a magnetic drill to be mounted onto ,some magnetic drills have a central coolant delivery system which pumps coolant down through mulitiple holes in the flutes of the drill, the carbide tips can also be replaced, with speed adjustment in rotation and speed of depth ,this will create a process although expensive to start with should save on repair costs in the long run.

Good luck.

"The holes are drilled with Pneumatic hand gun (Chicago Pneumatic)"

He should not use a air tool, unless it has a RPM reducing gear in it. A heavy electric tool or new generation battery screw- drill would work better. (Makita/Bosch e.g)

A drill bit that is cutting tends to heat less than one that is rubbing, use more pressure and lower speed. I worked with an old blacksmith that showed me that he could drill a spring leaf with a carbon drill bit using slow enough speed and sufficient pressures and lard as a coolant. In your case your drilling lube/coolant is insufficient for the task in quality and or volume. Take this bit of advise before you call me foolish. Use WD 40 as a lube and coolant either the aerosol can with nozzle tube or a pump sprayer and keep it applied while drilling. You will be surprised at the quality of drilling using this for a coolant/lube. Drill bit life can be extended up to 5 times or more with this technique and I may add that I did not discover this technique but discovered it from a supervisor in a big hole shop in our major city. (big hole shops specialize in drilling metals) They also were amazed and very happy with the results using the famous WD 40 product..( not an official endorsement) Remember the pressure must be constant while drilling any rubbing will remove the cutting edge very quickly.

Lyn,techmad & dvmdsc

I agree we can't get Concentric or cylindrical hole with hand drilling.

The size of aerospace jigs is huge. Many details are positioned on the frame / Structure of the jig. It is not feasible to jig bore these holes on the structure. So the details will be checked with Laser tracker (portable CMM) and hand drilled to 8H7 or 10H7 Holes and located with dowels (hardened cylindrical pins). In my Short span of experience, this seems to work reliably.

May be, as Maurie told abt magnetic drills, i have to find a equipment to meet my application and eliminate manual drill to get proper H7 Holes

Finally what we did was simply took the part and drilled in drill press (fortunately we could do in this jig despite some misgivings i had on " on assembly dimension").. i will take care of the advice abt coolant/lubrication, Speed and feed rate

Roy Hammy .. Thanks for the WD 40 Tip and definitely will try it!!

Use of WD-40 not! Go to your tooling supplier such as MSC or others and get a product called Cool Tool (or similar) with mist type applicator. Or better yet contact a tooling engineer from one of the many companies that supply the correct type of tooling for this work They will advise you on proper methods and materials. Kinematic, etc;

I was also wondering why the HSS drill bit is unable to drill the 30 HRC pin.. because before heat treatment, i consulted the cutting tools engineer who said HSS can drill materials with hardness up to 35 HRC!!

is there any other factor to be considered for machinability of the materials... What am i missing?? Don't want to repeat the mistake

Thanks a ton guys for all the replies

Cheers

Sengo

It may be a stupid question but why arent the holes drilled before hardening? Even if they are slightly under sized, reaming to correct size should be relatively simple compared to full boring.

Its a valid question and given the rework circumstance of the fixture, it was ruled out.

When I was at the shipyards (navy)........ We cut some what I would consider exotic materials....... Some I had a very hard time with getting MSDS sheets for them........ But on the difficult material, we would contact a tooling rep with the problem, and they would be happy to demonstrate their 'superior' :/ tooling. Some were some weren't.