Drill time

[kirki]

Guys I know this is a PLC website and iam asking general questions.. Please excuse me. I am trying to figure out the drill time required on a plate which has multiple rows of holes to drill and tap.

1.Drill(ft)=No Of Holes*(Thickness Of Sheet))/12
2.Drill(ft/min)=Spindle r.p.m (rev/min)*Feed(inches/rev))/12
3.Drill Time(hrs)=((Drill Ft / Drill Ft/min)/60)

Is this right? if not how and if it requires tapping then same formula should apply correct? Your advise will be appreciated.

[bernie_carlton]

Do you have an allowance for move time between holes or is this purely the actual drilling/tapping time?

[kirki]

Yes Bernie I will have time for indexing between holes . I will add up that later.

[Steve Bailey]

In your calculation for Drill(ft) you only calculated the distance the drill travels once its full diameter is drilling. It must also move the distance from where the point of the drill first contacts the sheet until the full diameter is involved.

[kirki]

Originally Posted by Steve Bailey

In your calculation for Drill(ft) you only calculated the distance the drill travels once its full diameter is drilling. It must also move the distance from where the point of the drill first contacts the sheet until the full diameter is involved.

For example 1" plate has 120 holes. The Total drill depth is 120" = 120/12 = 10 feet of drilling reqd..
Spindle r.p.m is 1000 and feed is 0.003 inches/ rev
1000 rev/min* 0.003 inches/rev = 3 inches/min (ie. 3 holes) = 0.25 feet/min

So now 10ft / 0.25 ft/min = 40 min..

[James Mcquade]

Don't forget that every linear foot of metal is different.
There will be hard spots in the metal at times.
You also need to consider the fact that drill bits get dull.

Are you using guided drill bits for your operation? Drill bits
will walk as they start to drill into metal.

In regards to tapping, you will not be able to tap at 1000 rpm. taps require much slower speeds (less than 100 rpm).
Are you going to use an automatic tap reversing head or stop the tap and then reverse to back the tap out?
you must also consider taps get dull quicker than drill bits.
what is your drill / tap fluid system?

regards,
james

[Steve Bailey]

A drill bit drilling through a plate looks like this:

         __   ______________++

 |      |

 |      | P      Plate

 |      |__   ______________

  \    /  

   \  /   x

    \/  ____

Your calculation only takes into account the "P" distance. You neglected the additional "x" distance that the drill has to travel.

[kirki]

Steve - you are right I'am going to take that distance into account.

But another question in my mind is why should i be even worry about the spindle r.p.m

The Drill Time(hrs)=((drill (Ft) / Drill Ft/min)/60)

• Isn't this enough to calculate time
• (OR) i have to do this

Drill(ft/min)=Spindle r.p.m (rev/min)*Feed(inches/rev))/12
Drill Time(hrs)=((Drill Ft / Drill Ft/min)/60)

I'am confused now

[leitmotif]

Originally Posted by kirki

Steve - you are right I'am going to take that distance into account.

But another question in my mind is why should i be even worry about the spindle r.p.m

The Drill Time(hrs)=((drill (Ft) / Drill Ft/min)/60)

• Isn't this enough to calculate time
• (OR) i have to do this

Drill(ft/min)=Spindle r.p.m (rev/min)*Feed(inches/rev))/12
Drill Time(hrs)=((Drill Ft / Drill Ft/min)/60)

I'am confused now

Speed is basically RPM
Feed is advance (or depth of cut) per Revolution.
All cutting tools have a certain speed and feed. Going outside of the "boundary" results in rapid wear or breakage.

You can do all the math you want and all the programming you want
BUT if you do not understand what the cutter operating performance is all is for naught.

From sounds of it you need to
1. Purchase a copy of Machinery Handbook
2. Consult with a machine tool distributor for proper setup of this process.

Dan Bentler

[Steve Bailey]

When tapping you must specify feed per rotation of the spindle. Otherwise, you get a poor quality thread and possibly a broken tap. When you use the same spec for drilling you get a consistent amount of metal removal over the full range of spindle speeds.