Saturday, June 16, 2012

Holding material down without a vacuum table.

Using a CNC has got to be the easiest form of woodworking. I once heard another CNC user say "I can't find a hammer that fits my hand." At the time I didn't get the joke but there's allot of truth there. I got a splinter the other day for the first time in what seems like years. I barely handle the materials i work with, and when i go to the local Woodworkers Club meetings, I make it a point to let the real woodworkers know that i have none of their skills. I know I have a hammer, I used it the other day to  break apart some trash before it went in the dumpster.

Unlike other forms of woodworking, there is very little "holding" the
wood. When your using a hand tool, or even a power tool, there is allot of handling, gripping, and otherwise touching whats being worked on. This make a lot of sense from a hand-eye coordination point of view, but when there is machinery involved, cold, unfeeling, one tends to think of how hard it might be to eat pizza with only one hand worth the fingers. But that doesn't mean the material can't be held in place, just that it needs to be done without your hands being involved.

With automated machines, there are several methods for accomplishing what is called "hold-down." Soe methods include Vacuum, Clamps and T-Track, Adhesives, and Screws.

Really fancy machines often have an option for Vacuum clamping. This is essentially a Machine with a tabletop that literally sucks the material tight to the surface. It's not always great with small parts, but by and large its pretty dang effective. First time I saw one in use, the operator tossed a piece of scrap wood on the cutting surface and i couldn't for the life of me get it off until he turned off the suction. Here is a demonstration of just how powerful vacuum clamping can be using a setup on a work area.

Clamps and T-Track is pretty standard on a CNC machine, if it has anything for hold down, it often has this aswell. This setup work by having metal slots in the table which allow bolt head's to be inserted down, and a nut is threaded to the bold pressing down a "clamp" (typically a small block with a hole or slot in it's center.)

Some projects require adhesives, possible because the object is very small, or because there isn't a place to actually "hold" the material except underneath. I most often use this when working with styrofoam.

There there are screws. This is the poor man's route. Well, let's be honest, I don't have t-tracks, and sure as heck don't have a vacuum system. While this system probably takes the longest to setup, its probably the strongest method for holding down materials. There is a trick.

Screws are metal, and if the cutter hits one, your likely going to have trouble. Broken bit, chipped cutters, or worse, the bit survives, but the machine is thrown out of alignment and cuts all over the place.

When I first started working with entire sheets of material, i would literally crawl onto my machine while it was running, and start screwing the material down while the machine was going. I always had the material held down from the edges, but it it bowed and needs to be held down in the center aswell. So while the machine was running i'd stand onto, and when the machine had cut stuff in one region, and i knew it was safe to place a screw, i would insert a screw while the machine was out of the way. The one day i had a better idea.

Why not pick safe places for screws before cutting the parts? Well, there is a trick.

Once you have your designs all programmed and your ready to get cutting, do one last step. I take my circle tool and place circles with a diameter of .3" (That's about how big the head of a typical wood screw) between parts where its out of the way of the cutter. How many? Well, that depends on the shape and size of parts on the board, where they are positioned, etc. However, when i am doing it, i try to get atleast 9 or 12 screws into my material in addition to the screws a the edge.

 Selecting all the circle place, I create a drilling tool path and use a .125 (1/8") bit to pre-drill all the screw holes. Run this operation first, screw it in place and then run the cutting file. This has saved me tons of time scrambling over my machine while its running to place screws, and it still doesn't look like I am getting vacuum hold down any time soon.


Elizabeth J. Neal said...

This will make the more reviews vacuum even better.Slowly pull the hose out of the bag.

Richard C. Lambert said...

FSJ vacuum routing can be daunting to look at. Here's a quick rundown on routing for a mid-80's FSJ. Different model years used slightly different vacuum routing. See links at the bottom for a great site on vac diagrams for various model years.James C. Moon

Unknown said...

You are interested in the best shark vacuum, please Click Here

Elizabeth J. Neal said...

thanks this is good blog. Best Steam Mops for Tile Floors

Elizabeth J. Neal said...

I can see that you are an expert at your field! I am launching a website soon, and your information will be very useful for me.. Thanks for all your help and wishing you all the success in your business. Homepage

Lynna Conner said...

Intriguing post. I Have Been pondering about this issue, so much obliged for posting. Really cool post.It "s truly extremely pleasant and Useful post.Thanks

Rahul Singh said...

Your site is very informative and famous site I would like say that your articles is very interesting and different other sites.
biosafety cabinet

Rahul Sharma said...

This is really a nice and informative, containing all information. Thanks for sharing it. filter papers

Cindy said...

Learn more info about best vacuum for your floor here:

mtom said...

The the next occasion Someone said a blog, Hopefully it doesnt disappoint me just as much as brussels. I mean, Yes, it was my method to read, but When i thought youd have some thing fascinating to convey. All I hear is really a handful of whining about something you could fix when you werent too busy trying to find attention. Dewalt Dws779 vs Dws780

Dolpphin said...

Great post, I would include that 'Extraordinary synthesis is a pleasure to the eye' as well; that is the reason we have each one of the styles and outline slants to make it is a pleasant. Undertaking for readers.
pest control services in Delhi
pest control Gurgaon

Melbourne Vacate Cleaning said...

Very well written post. You have shared a wonderful article which is very helpful. Thanks for sharing, have a good day.
End of Lease Cleaning Melbourne

Unknown said...

It was a decent post to be sure. I completely delighted in understanding it in my lunch time. Will definitely come and visit this blog all the more frequently. Much obliged for sharing. Best Hospital in Hyderabad

Prathima Hospitals said...

Great post. I would include that 'Extraordinary synthesis is a pleasure to the eye' as well; that is the reason we have each one of the styles and outline slants to make it is a pleasant. Undertaking for readers. best hospitals in Hyderabad

Mothertobe said...

Very nice post I really enjoyed it...You can also visit my website for.
Best Fertility Centre In Hyderabad

Prathima Hospitals said...

This very nice and wonderful article thank you for share this information. I really impressed this article.
Best Bluetooth speakers under 2000

Settle Via us said...

Thanks for sharing this amazing blog with us, I have found lots of interesting stuff on your blog. well done guys and keep up your work.
Student Visa Australia
Skilled Visa Australia
482 Visa Australia

brittanymlemay said...

Hey what a brilliant post I have come across and believe me I have been searching out for this similar kind of post for past a week and hardly came across this. Thank you very much and will look for more postings from you. PalandSmith

Ravi Sharma said...

Such a great post you share with us, I really appreciate your work and content idea and I have found here lots of knowledgeable information this website perfect for my need.
nitrocellulose membrane