help with a estimate.

[knight_toolworks]

Ok so I am bidding on for me a large job. 500 sheet of 1/4" mdf cut into circles with holes.
the pic does not show it but there is only a small amount of material left around the parts and there are two waste rings and a center circle that is scrap. I pocked them out to show whats left the rest is scrap. so what I need to work out is how much scrap I will have. I have a 2 yard dumpster how many times will I fill it.
I can cut at 6ips with a 5/32" downcut bit I need an idea of how many I will use up. I seldom cut enough of the same part/material to really get an idea of bit wear.
there are a few missing rings in the picture but you get the idea.

http://dl.dropbox.com/u/1939753/rings.jpg

[curtiss]

Looks like three different size rings.

If you can send the size/ width and number of each ring on the sheet, I can plug them into AutoCad and get the areas for you.

I assume a 1/4" bit ?

[knight_toolworks]

here you go. I will be using a 5/32" bit. 97x49" sheet.
http://dl.dropbox.com/u/1939753/rings.DXF

[dlcw]

I cut a lot of parts from 1/4" and 1/2" MDF for a customer and use a 1/4" compression bit. I am getting about 4000-4500 linear inches of cutting before I start seeing cut quality go down. I just figure out the number of linear inches I was cutting and figure the number of bits based on that.

As far as dumpster material, figure out the approximate square inches required for each part you keep, subtract that from the number of square inches in the sheet and you have your waste per sheet that has to go to the dumpster.

[curtiss]

Per your drawing I get,

92.34 sq inches for the large ring,
45.9 sq inches for the middle ring and
18.65 sq inches for the small ring.

Not sure how to do the dumpster calculation. :confused:

[ken_rychlik]

I would worry more about the time estimate and getting my hourly fee along with a bit and handling charge than what the dumpster would cost.

Maybe you should charge X ammount per sheet for waste and give them the option to pick it all up.

[dlcw]

Dumpster calculation is (total sheet square inches minus square inches of material used for finished parts) times the number of sheets you are going to process.

For example there are 4753 square inches in a standard 97"x49" piece of MDF. Per the numbers Curtiss provided there is 156.89 square inches in parts. Multiply that times the number of parts per sheet. Now you have your total square inches used for finish product. Subtract that from 4753 and you have your dumpster number.

Use Aspire/Partworks to calculate your cutting time and multiply this by your CNC rate. On straight cutting (not 3D modeling Aspire/Partworks are fairly close at estimating time.

My machine rate is $1.00 per minute retail and, depending on volume anywhere from $.50 to $.75 per minute wholesale.

[mark_stief]

wish you were closer mdf make a good pellet grind the scraps and make pellets

[knight_toolworks]

I actually ran an aircut to get the exact time. way too many sheets for a somewhat on software guess.
I did a test cut to see if I could cut the parts at 6ips I don't usually cut that fast.
I gave up my weekly dumpster dump as I would not begin to fill it when it was slow. but I may just do the weekly thing and add it to the total. bits are what I am not sure of. I will use three hours of cutting per bit to calculate it and charge that amount. but I am thinking of cutting 1/4" into the spoil board so I can get double the life out of the bit.
right now I will be charging about 70.00 a hour.
but this is a big job and even if I cut 6 hours a day it would take about 1.5 months to cut them all. but I have other customers so I can only see cutting 3 or 4 days a week. they might not go for that.

[myxpykalix]

Let me ask a dumb question...based on your picture, if you cut out these inner rings first, outer rings last how are you holding them down?

[knight_toolworks]

between the vacuum and more important a small downcut bit it is not a problem. that's the key as small of a downcut bit as you can get away with. packing the sawdust inot the cut is key to holding them in place.
But I don't think I will get the job they want it in about a month and even if I cut 6 hours a day 6 days a week it is almost 2 months solid of cutting.