Combine G73 and G83 Peck Drill Cycle!!

[khalid]

Currently drilling lot of holes on Stainless steel tube sheets and baffles... I am using HSS drill 8mm, 9mm and 10mm with great success so far.. Currently my strategy is using G83 for thorough hole 65mm deep in stainless steel and then enlarge these holes in second operation by using G73 cycle and using 10mm drill..

Now using G83 with Q=2mm for a hole of 65mm deep it gets 12minutes that is a lot of time... Is their any possibility i use G73 for a half of that thickness and then continue the same hole with G83 peck drill?

Any thought or suggestion?

[BR549]

It is done all the time (;-) When drilling tube we also use another trick drill throught the top section then reset the R level just above the bottom section that way when mach drills trought the top it will rapid done to the next level and continue. Savea all that drilling air.

Just makes sure to reset the R level when you have completed the hole OR you will snap the bit whn Mach tries to move at the low Rlevel inside the tube.

G73 X0.000 Y0.000 Z-0.1 R0.100 F10
Z-1.000 R-0.900
R 0.100
G80

[BR549]

OOPS that should have been

G73 X0.000 Y0.000 Z-0.1 R0.100 F10
Z-1.000 R-0.900
Z.1R 0.100
G80

OR
G73 X0.000 Y0.000 Z-0.1 R0.100 F10
Z-1.000 R-0.900
G80
G0Z.1


ALSO you may want to try a cobalt bit instead of HSS.

[BobWarfield]

+1 on the Cobalt bit if you have a lot of stainless.  Could even be worth a carbide twist drill.

Cheers,

BW

[khalid]

Thanks BR549 and Bobwarfield...

BR549 .. i will see how this comes out... Initially i was thinking to use G73 for half of the thickness and end it with G80, and on the next i use G73...However your idea seems to be applicable...
Bob...I tried HSCO, HSS and Carbide drills so far... HSCO and HSS  gives me almost the same results. No good luck with HSco... I wonder how peoples drill 1000 of holes in SS without sharpening the bit???
 My strategy is...For every 10th hole i have to pause the machine and sharpen the drill...Currently only using HSS...


http://www.youtube.com/watch?v=FH2X_W2MHBY&feature=email

[BobWarfield]

Bob...I tried HSCO, HSS and Carbide drills so far... HSCO and HSS  gives me almost the same results. No good luck with HSco... I wonder how peoples drill 1000 of holes in SS without sharpening the bit???
 My strategy is...For every 10th hole i have to pause the machine and sharpen the drill...Currently only using HSS...


http://www.youtube.com/watch?v=FH2X_W2MHBY&feature=email

Khalid, 65mm is a pretty deep hole with a 10mm drill.  Nevertheless, it should be doable.  Your enemy will be work hardening on stainless (most alloys, anyway).  Because of that, you need to keep the feedrate up, correct spindle speed, and plenty of coolant.  I don't what your spindle and feedrates are, but G-Wizard would go with 280 rpm and 30 mm/min feedrate.

Be sure you don't let the twist drill dwell or stop feeding while in contact with the stainnless.

It's pretty tough to do a lot of holes in stainless without carbide.  With a carbide bit, you could run 1100 rpm and 145 mm/min feed.

Cheers,

BW

[BR549]

BOB is correct, working with stainless can be painfully slow as you cannot dwell AND speeds are critical. We found cobalt to be the best compromise of cost and durability working with oddsurface shapes such as tubes.

It far outlasted HSS and cost much less than GOOD carbide. 

BUT if it were a high production and cost sensitive CARBIDE all the way and run as fast as possble

[khalid]

Currently for HSS drill my RPM and Feed as follows:
Spindle RPM= 800 RPM
Feed= 25mm/min (1 IPM)
DOC per peck=2mm
Using Flood Coolant.

The above Feed and Speed was kept for HSco and both HSS and HSco last for 15 holes , so as a rule of thumb i modified the gcode for tool change afte each 10 holes... We have Tool and Cutter grinder.. We achieve the drilling through HSS by keeping the Rack tip angle 140 degree..

Following is our sequence:
A) Centre drilling all holes upto 3mm depth with 4mm HSS centre drill... All 224 holes without resharpening
B) Intermediate hole with 8mm HSS drill... G83 cycle with Q2 --- Flood coolant with 3 jet nozzles
C) Final drill 10mm HSS drill.... G73 cycle with Q2--- Flood coolant on

The tubesheet is 30mm thick solid piece..
The baffles are 3mm, total 18mm stacked with welding..total thickness 54mm...

[BobWarfield]

Too many rpm, too much feed for HSS in stainless.  A quality HSS twist drill from Dormer is recommended to run at 50 SFM or so.  You're running at 82 SFM.  You want to slow down even from the recommended for the deep hole, and if you're not using a quality twist drill.

Try the figures I recommended above.

Best,

BW

[khalid]

Thanks Bob for reply and advice...I have drilled holes in baffle yesterday..
I was running the controller on 24Volts so my rapid was very slow..I kept the Z-axis Rapid 10IPM and i can't exceed 16IPM because of loosing step... At these voltage parameters and G83 cycle one hole 60mm deep took 12minutes..
Yesterday I increased the voltages to 48Volt and my rapid increased to 25IPM and the same hole were done 5minutes per hole with G83...
Tommorrow i will further increase upto 60Volts as my controller and motors can bear upto 80volts and 110 volts respectively...

I also want to get red of the round column and Quill, so making my own column and spindle as you can see in the pictures..I have machined the column and now ready to drill holes for linear Rails..I machined exact slots for the width of linear rail on a NC boring machine... The base and the column are perfect at 90 degree...
Meanwhile, the spindle grinding is now in action after hardning upto 55HRC...


PS:
Can you repeat the Feed and Speed for HSS and HSco drills 8mm dia.