Newbie Question re: What machine and pieces per hour

Hi guys (and girls) am researching potential machine to run similar parts as the attached picture. Essentially it is several circles cut out of a 4x8 sheet of 3/4" plywood, along with 30 - 1/2 dia. holes.

Not familiar with CNC routers and not sure what type of machine would be required in a production setting (m/c running 8 hours per day) and approximately how many 4x8 sheets could be processed in a days shift.

As always cost is a factor which is why the Shopbot PRsalpha models look promising versus an expensive Multicam type brute.

Hopefully someone can make some machine recomenedations along with approximate parts per hour.

Thanks for all the help.

Here is the question, that you 1st must answer. How much are you looking to spend, and what is going to be your run time, because there is no way a shopbot is going to run 8 hour continuous, and new machine may start off that way, but if you are going to run these types of items and hours. You are going to need the BIG IRON...and there are plenty of used machines out there, that for what a new ShopBOT cost, you can get a used CNC, Vacuum Pump and Software for what the 5x10 machine runs. Check it out here are couple of websites..

www.cncfactory.com
www.xfactory.com
hell even ebay.com

You can even put in the contract, they the purchase is based on the machine running correctly or they repair the machine at their cost or you can ship the machine back for a refund, I have installed two machines, with these types of contracts.

Thanks for the help MCPservice.

Related to budget between 20-40k, maybe 50k if capacity and capabilities warrants.

Related to run time, trying to calculate that out which is dependent of the machine capabilities and approximately how many pieces per hour the machine can handle. As you state "Big Iron' type machines, if we assume a run of the mill, middle of the road "Big Iron" m/c what would be your best guess to pieces per hour for the item I am looking at routing assuming the bed is large enough to cut a 4x8 sheet.

Just browsing thru the links your provided, very interesting, was not aware they existed. Many units available I see with very reasonable prices as well.

I took your pieces and created them in Enroute, and punch your 1/2"holes with a 1/2" endmill at 200 ipm @ 18000rpms, and cut the circles out with a 3/8" endmill at 400 ipm @ 18000 rpms. Now mind you I did not have a correct length defined in the tool library and I did leave a onion skin of .045 to maintain vacuum, but it looks like the est. time is going to be for a full sheet approx. 13-15 mins and that time can be modified, it is possible to cut the sheet out faster, if you choose the cut order to cut in a more logical manner.

If you have anymore question, please ask.

[email protected]
Chris
678-548-1483

www.mcpservice.com

If you do decide to purchase a used Multicam machine, please give me the opportunity to discuss with you how MCP can meet your installation needs..

A machine with a drill head would be preferable, as plunging 1/2" holes all day is not good for the spindle. Also, are you making a single cut between two parts, or cutting each part separately? With a single cut, you may get finish quality issues. Depends a bit on the quality of the plywood, though.

Holding the parts down can be tricky, especially with the quality of plywood today. If it's not dead flat, vacuum won't hold parts that size. And the plywood we get starts warping as soon as we cut the bands off.

Depending on the type of plywood, I'd be cutting it at around 800ipm (on a Morbidelli with 15HP spindle). If I was able to keep the parts from moving without onion skinning, I'd say around 5-7 minutes a sheet, maybe 10 minutes with onion skinning. Loading and unloading can take a lot of time, and needs to be considered. It'll probably take nearly as long as actual cutting.
With a machine capable of 80ipm, a good operator should be able to do at least 50 sheets a day. With our Morbidelli, I could maybe get closer to 75-100, but it has a rake to unload the sheet and clean the table, so only about a minute to unload and reload. Probably out of your budget, though.

It doesn't look llike you accounted for the router bit diameter in your drawing. You will not get 2 48" circles from a 4X8 sheet of plywood unless you get sheets that are somewhat oversize.

While you can program this at 800 IPM, I doubt that it'll run that fast. I just did a bunch of stuff with 3/4 (18mm actually) baltic birch and learned a few things about cutting that crap.

I suspect that your main issue will be part hold down, even with vacuum. Plywood is a bear to work with unless you build a dedicated fixture for the parts.

Another question you need to answer is how much you can afford to spend per part for machining. It may be that a lesser cost machine running slower will be the best option.

Getting someone else to run the parts may be an option, at least at the beginning.

Where in Canada are you?

Thanks for the response which I will go thru one at a time

MCPservice, first I will definitely be in touch with you as have some information/question to discuss in private. 10-15 minutes per piece (4x8) sounds very reasonable. Another thing very curious about is the actual method to hold down such a piece, as it is essentially several narrow rings. Spoke with some local guys yesterday and one mentioned that no matter with what ever route you go make sure you get at least a 9 hp vacum pump, the one he mentioned directly was a 9HP 3Phase 25"Hg 171CFM 750Lbs Vacuum Pump with
filter, valve & starter. After reading these new messages and researching really hope the system I come up with will be able to hold down this type of set-up and not have to buy something else cause I did not research enough.

Was thinking worst case, and this might not be feasible, is to incorporate both a vacum hold down system and mechanical clamps on the outside corners and center, and machine outwards from the center. Rather not have to plan for any sort of seconday operation to trim this "onion skin".

Notice from broswing the ex-factory listing, the smaller models but still 4x8 or 5x10 use a 3-5 horse spindle, medium is 5-10, and the larger units (most expensive) use 10+.

Quote:

---

Originally Posted by wguttrid

Notice from broswing the ex-factory listing, the smaller models but still 4x8 or 5x10 use a 3-5 horse spindle, medium is 5-10, and the larger units (most expensive) use 10+.

---

We have noticed that even with the proper bit and depending on the feed rate a 7hp spindle can have trouble with 3/4 plywood.

Dropout, I am located in Ontario. How about yourslf?

Related to my cad example posted, table and hold down (fixturing, clamps, vacum) recommend or best guess be to steer me in the right direction.

Were you to finally tweak your machining process with 3/4" plywood material after some trial and error to where you were happy with end cut and time?

curious what is the solution to onion skinning if required for vacum to hold down, is it a matter of making a second cut to remove the last bit of material or is it removed by a secondary process/machine?

Quote:

---

Originally Posted by wguttrid

curious what is the solution to onion skinning if required for vacum to hold down, is it a matter of making a second cut to remove the last bit of material or is it removed by a secondary process/machine?

---

Depends on how good your vacuum is, and how flat the plywood is.

When I cut 3/4 melamine, I leave a .008 onion skin and recut it on the machine. I do this for parts less than 250 sq. in.

You need to leave a thicker skin with plywood, as the vacuum will leak through. If the sheet is flat after the first pass, you can probably cut the second pass on the machine. I try to use a .1 onion skin. Keep in mind that part size plays a very big role. Condition of the spoilboard comes into play as well. It'll hold better when freshly surfaced than when it starts getting a bunch of grooves in it.

Since you'll have 5-10 minutes per sheet, you'll probably have time to leave a thicker skin and hand cut the sheets with a laminate trimmer. But you'll get a better cut on the machine with a compression bit, as plywood will get frayed edges.

We have two 25HP Becker pumps on a 5x12 table. But we get a lot of leakage when cutting 4x8 sheets. A 9HP Pump should be OK if it's set up for a 4x8 zone only.

As far as spindle HP, if you have an ATC, here's a good option if you have lower HP. Use a roughing pass about 5/8" deep, 1/16" oversize with a roughing bit. Then make a second pass all the way through with a compression spiral. Roughing bits can cut much faster with the same HP, but they don't leave a smooth edge. This can extend the tool life of your compression bit by up to 5 times or more.

Spindle HP, you may want to consider 10hp spindle or higher is possible. I know it can get costly, with a bigger spindle, but you will be glad that you have a higher hp spindle, I can take a 10hp Eurospindle with a Onsrud 60-123MW and easily cut at 400ipm@ 18000, and can push it faster with not problem, then come back and cut your onion skin at say 200 ipm, now if the plywood is warped, a fixture may not be a bad idea, in addition to a 20hp PD vacuum pump to assist with hold down.

OH....and yes I was accounting for the material being slightly over sized 97" by 49".

Vacuum: if you can find a 20 hp PD, with a machine package it is great hold down, specific for panel processing.

PD= Positive Displacement Pump

In choosing a used machine, make sure you do an inspection, hire someone to make sure the machine is mechanically/electrically sound, take pictures or video if the machine is still under power, make sure the contract has some provisions for repair or return.

I just recently had to stop an install because the customer did not know the machine is wired for 440volts, vs the standard 230 volts. They are kind of lucky, there are other buildings in the area that have higher incoming voltages, that they are going to be able to move into.

Their other opinion was for me to change out about a half dozen components, approx 3200.00 for parts alone, so make sure you get a SN# and call the manufacture, a lot of times all the info you need is tagged with the SN#numbers.

A little research goes a long way.