Gundrilling "Hardox" abrasion resistant plate

[glassguy]

I just got an RFQ for gundrilling a .312 diameter hole in material called "Hardox" (by Oxelosund) which will be at 50 Rockwell. Their website is not helpful about this process. Any suggestions about quoting (or not)and drilling (or not) will be appreciated. There wil be only six pieces with two holes each, just over 5" deep, but the plates are 165" long (i.e.: not cheap to replace if scrapped). We are a small gundrilling jobshop with 16 spindles (all real gundrilling machines) for various types of workpieces.
- Thanks

 

[Viktor]

It is possible, in principle. However, if I were you, I would not take this job. It is not worth the effort you have to apply, unless you have special gundrill in the house. Who is your regular gundrill supplier? What grade of carbide you have currently?

Have a look at my page

http://gundrilling.tripod.com

Viktor

http://viktorastakhov.tripod.com

 

[EdDanzer]

We have machined 500 BNH plate very successfuly using carbide insert drills with oil and ceramic inserts dry for milling. We found 2 stroke motor oil best for insert life on the insert drills at 100 surface feet in a HMC. We were through drilling 5/8" plate with 23/32, 1 1/32, and a 2 3/8" diameter drills, and finish boring the 2 3/8 to 2.500.

 

[Viktor]

Would you please explain your
“drills with oil and ceramic inserts dry for milling.”
What was the material of the plate?

Thank you Viktor

http://viktorastakhov.tripod.com

 

[glassguy]

I now have a sample piece of HARDOX to try. Since we're a job shop, we try 'most anything!
Viktor - I suspect you already know the answer to your question about what grade of carbide we use. Since we're jobbing as gundrillers, we rarely have the luxury of buying drills with non-standard carbides for jobs. We have over a thousand gundrills on hand from most domestic manufacturers and a few from Botek. Some of these drills were bought at auction (a poor practice if you're going to drill a long series of parts, but a great way to flesh out a collection!) which gives us quite a resource. Some of them don't even have mfg names on them.
But, our .312 diameter drills either came from Eldorado or Drillmaster.
I'll let everybody know how the test went. Thanks for your input.

 

[glassguy]

The test drilling was worthwhile; we learned enough to know we can drill the holes. Having experienced operators certainly pays off!
Thanks again for the thoughts; I won't hesitate to bring other questions to this forum.

 

[Viktor]

glassguy

Would you please share with us the rpm, feed rate, and type of coolant you used for the test. What was tool life (in)?

Thank you
Viktor

http://viktorastakhov.tripod.com

 

[EdDanzer]

When we mill hard material with ceramic inserts we use Kennametal SNG433T K090 at 300 SFM and .001-.002" feed per tooth without any coolant. When milling the chips come off glowing yellow/red, and some times burn. There may be newer grades that work better. We will be milling and drilling some 500 BNH plate in the next week or 2 and may try some new grades of inserts.

 

[glassguy]

To start, we went with the manufacturer's recommendation times three.
We use a generic gundrill oil and drilled a few holes on our Mollart which would drill the job if it comes to pass.
The .312 diameter drill was from Eldorado. Standard carbide. At 1/8 feed with a 30-20 grind, about 2.5" per sharpening, but 4.5" with a 20-20 grind. The hole tightened up at 1/4 feed and the corner got rounded. In each case, the land showed excessive wear - this is tough stuff, after all!

 

[Viktor]

glassguy

Thank you for your valuable info. I will appreciate if you tell me the relief angles on the outer and inner cutting edges, the coolant flow rate (or the drill length and coolant pressure which is almost the same). What was the size of the cylindrical margin and did you use the addition relief angle at the margin? I assume that you used a standard Eldorado sharpening fixture and Eldorado point grind. Am I right?

Thank you
Viktor

http://viktorastakhov.tripod.com

 

[glassguy]

Viktor:
I didn't see your last question to this forum until today. I know how interested you are in all aspects of gundrilling, so I'll try to answer but it has been a while.
The coolant pressure was high as it would be on any gundrill, I suppose. Probably over 1000 PSI. I suspect that he used the shortest drill he could (22"?). The sharpening fixtures we use are Eldorado's, but I can't be more specific than the angles noted before. The guys try what they think will work based on experience more than charts and seem to do all relief sweeps by eye.
I don't know if this is helpful or not, but it's the most I can offer at this time. Again, thanks for your input and, FYI, in the end, we didn't get the job even though we were successful in our testing!