Calculating Time of a Peck Drilling Cycle on Milling Machine

[InMFG]

I am looking for a formula to calculate the time of a peck drilling cycle. I have several deep holes to drill in a job I am quoting. I am looking for a formula that I can enter in these variables: hole depth, peck size, drilling feed rate, Rapid feed rate, clearance amount. This cycle retracts from the hole after every peck, and returns to the "clearance amount" at bottom of hole.

Example of variables:

Hole Depth: 25"
Peck Size: .125"
Drill Feed Rate: 3 Inches Per Minute
Rapid Feed Rate: 150 Inches Per Minute
Clearance Amount: .020"

See attached picture for clarification of cycle.

 

[ornerynorsk]

The only unknown is your machine's acceleration/deceleration ramp for rapid-to-feed transition and direction reversal. Other than that, it's just adding up the numbers.

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.

 

[InMFG]

Machine acceleration/deceleration is minimal and not even a factor to bother with for my purposes. I don't see how I can just add up the numbers. The problem is calculating the distance every time you peck, you retract all the way out of the hole and then back in. That distance will increase every time you peck. I want a formula that I can use with different variables.

 

[ornerynorsk]

If you divide the hole depth by peck/step travel, that will give you the number of pecks. In your case, 25 inches depth / .125 = 200 pecks. You will likely end up with a short peck due to the 0.020 clearance, as the machine will feed that distance instead of rapid, and it will not exceed 0.125 per peck. Rapid time must be included for this peck.

So 201 pecks with a total feed distance of 25.020 inches, multiplied by your feedrate. Then, you will be rapiding between 0.020 and -25.000, so take the average of those 2 values (12.510 inches) and multiply by the number of pecks, divide by the rapid rate, and that will equal your total rapid time.

You can easily put together a spreadsheet in excel to plug in your variables and arrive at an answer.

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.

 

[ornerynorsk]

Be sure to account for rapid in and rapid out on your average distance. For all practical purposes, you can use the value of your total depth, and just not multiply it by 2 for both the in and out travels, but I personally like to treat it seperately. It stays more well organized in my mind that way.

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.