Plastic scanning beads at amazon-dot-com!

[Jim Wood]

I just went on a new search for quarter-inch plastic beads for a bead-disc scanner and found an unlikely source. Here's the page:

http://www.amazon.com/Acrylic-Polished- ... 03&sr=1-34

These are Grade 2, which is a cut above the ones I used to get for Doug Pitt from TAP Plastics up in northern California. Grade 2 generally relates to a dimensional tolerance and 'sphericity' of ±0.002", although sphericity of this part is claimed to be ±0.001". What's more, these are cheap, less than a nickel each disregarding shipping charges. The same Amazon-related firm <www> has these in different sizes as well, from 1/8" up to 1". Perhaps a 1/8" or 3/16" bead might be as good for NBTV, but generally the larger the better for passing light. If someone has more information on this subject (Doug knew this stuff), please post here.

Happy scanning,
-Jim

[Andrew Davie]

Looks like $1 each, not a nickel each!
Cheers
A

[Jim Wood]

I think the link got corrupted, it now points to a one-inch-diameter 'bead,' which might be good for a 10-foot disc, but the quarter-inch beads are $4.70 for a bag of 100.

[gary]

what's a "nickel"?

Thanks for that Jim, a very good find - I have not been able to source any in Australia at all.

I have one set from the NBTVA, which I believe you sourced, and treat them like precious artifacts...

[Jim Wood]

What's a nickel? Why it's a twentieth of a dollar, or 5 cents. Our pennies, or one-cent pieces, now cost the government more to make than they are worth. If you need a metal washer, just drill a hole in a penny, it's cheaper than buying the real thing at the hardware store.

If you guys need plastic beads, let me know. I can get these very easily and post them off to you cheaply. I would like to know if a smaller bead, say 1/8-inch (I think that's a hair over 3mm), would work as well as a larger one. The hole to accept a smaller bead might be easier to center and drill with less creeping.

[gary]

What's a nickel? Why it's a twentieth of a dollar, or 5 cents. Our pennies, or one-cent pieces, now cost the government more to make than they are worth. If you need a metal washer, just drill a hole in a penny, it's cheaper than buying the real thing at the hardware store.

If you guys need plastic beads, let me know. I can get these very easily and post them off to you cheaply. I would like to know if a smaller bead, say 1/8-inch (I think that's a hair over 3mm), would work as well as a larger one. The hole to accept a smaller bead might be easier to center and drill with less creeping.

I certainly want some, I just went on to Amazon to buy them but hesitated when I found out the shipping would be 3 times the price of the item, and that, with the exchange rate, brings the unit price up to about 30 cents AUD (still not that bad I suppose) and thought that maybe I should wait to see if the exchange rate, which is currently very bad, improves.

I am not sure, Jim, that you could post them any cheaper?

I too was wondering about the 1/8-inch beads for the same reason so I was going to grab a bag of those as well.

I am currently building a CNC router which I am hoping (perhaps fruitlessly) will be able to route the disk and holes very accurately, once that is done, and if it works, with cheap beads I can experiment to my hearts content.

[Jim Wood]

Gary, I just ordered a hundred each of 1/4", 3/16" and 1/8". Your CNC idea sounds great. I was actually thinking of creating a Gerber file in my PC layout program and have a circuit board house make a disc for me. Very expensive in onesy-twosies, however; if your CNC thing works out, I'll be a customer straightaway! What material were you thinking of using?

Send me your address off-group and I'll post you 33 of the 1/8" beads. These were incredibly cheap, less than US$2 for 100, and doubtless will go in an airmail envelope at our 1 ounce rate. I didn't get them from Amazon, but from another online purveyor of miscellaneous hardware and related parts for experimenters, prototypers, etc. Check them out at www.smallparts.com. They have pulleys, belts, bearings, etc.

[gary]

Thanks Jim,

Technically, the machine should be able to route it in soft aluminium, acrylic, or wood. Initially I intend to experiment using thinnish plywood (or maybe even MDF) since I don't want to waste expensive material at least until I have proved the concept. Using beads should mean that I don't need to use particularly thin material (at least I can't see why I would), in fact the thicker the material the easier it should be to seat the bead.

The first iteration of the machine may not be accurate enough to place the apertures to the degree of accuracy required, but the idea is if it is not, the machine can be used to build another machine that is more accurate still...

In the end if it is not accurate enough, it still has many other uses so I think it is worth the effort.

I have built a scaled down prototype to test the steppers and electronics, built out of scrap wood etc. and it seems to work fine at that scale (about 12" x 9") but the larger they become the harder it is to keep the tolerances. I want the unit to be able to produce a 20 inch disk. The prototype has been dubbed "Frankenstein" by an observer because it is so ugly and has so many protruding nuts and bolts. The full size one should be prettier, but not too much so.

In theory the machine should be capable of 0.00025 inch accuracy, but that of course is assuming no play in the linear bearings, supports, etc - a very unlikely scenario - we shall see.

If it works I should be able to churn disks out like sausages - lol.

[AncientBrit]

Don't inhale the MDF dust Gary, supposedly vey unhealthy.

Regards,


Graham

[gary]

Don't inhale the MDF dust Gary, supposedly vey unhealthy.

Regards,


Graham

Very true, Graham, I use goggles and dusk masks/respirator, and have an extractor connected to all my woodworking tools: Table saw, router table, power sander, and various other powered hand tools, and I always keep the work area well ventilated.

MDF can be bad especially if made with formaldehyde, but that is not to say that other wood materials are not, in some ways they are just as bad if not worse. As in most things adequate safety precautions must always be taken.

Having said that, I think that a lot of us stand a much greater chance of being electrocuted than contracting anything from hobby level woodworking.

Cheers,
Gary

[AncientBrit]

Gary, re electrocution. Very true!

Regards,


Graham

[Andrew Davie]

Don't inhale the MDF dust Gary, supposedly vey unhealthy.

Regards,


Graham

I can vouch for this. I did some work in our kitchen a few years ago and promptly came down with pneumonia, which nearly finished me off. Wear GOOD breathing equipment.

[Jim Wood]

You fellows make MDF dust sound dangerous. I've been inhaling it for years and figured that's why I'm not getting any older, formaldehyde being the principal ingredient in embalming fluid.

[Kevin Hadfield]

Came across this page on the same website that sells the small televisor kit. Various size acrylic balls, but no indication of their dimensional precision. http://www.mutr.co.uk/product_info.php?products_id=125

[Jim Wood]

Those UK-source balls look to be pretty much the same thing as the ones over here, 3.2mm being pretty close to 1/8-inch. But 22p each sounds rather dear, about 8X the cost here. I'd be happy to obtain and post a club-size quantity if someone's interested in 'brokering' these over there... and no VAT!