Design News for Mechanical and Design Engineers

Dear Search Engineer: I'm trying to find a way to have data glowing through a tinted plexiglass window with the power of an LED. The font size is about 6 or 8. When a function is selected, an LED lights up. Could I use the LED to make the information glow? Could I use a fluorescent tape for this purpose?—J.R., Canada

Eh, J.R.: A simple light sanding or sandblasting on the plexiglass can even-out the light dispersion. There are also plastic filters either made or used for this purpose. Look at an instrument cluster in a low-end auto and you will see how it is done.

Dear Search Engineer: I'm looking for some plastic that can replace a porous bronze sleeve bearing. Any suggestions?— D.N., CA

Dear D.N.: First of all, great initials! I've got a couple suggestions to check out. RTP Company (www.rtpcompany.com) is a custom thermoplastic compounder that does metal replacement applications. A couple of ideas would be their Splash Lube Gold materials and PTFE-filled acetal material. Another possibility is replacing the bearings with Hycomp bearings. (www.hycompinc.com)

A couple of notes from loyal readers . . .

F.D. writes about the electrically controlled fiber optic devices in the July 7 issue . . ."While you suggested a large-scale routing system based on micro mirrors, I'd like to bring to your attention that Fibersense & Signals Inc. (www.fibersensefirst.com) provides a range of fiber optic, photonic, and electro-optic combining, switching, and routing components."

And W.W. offers this advice to D.J. on the size of a hex head also from the July 7 issue:

For both hex head cap screws and hex head bolts, the width across flats is 1.5 D where D= basic (nominal) bolt or screw diameter. For both the hex head screw and hex head bolt, the head height is 0.625 D minus 0.0 to 0.031, depending upon diameter, for hex cap screws and plus 0.0 to 0.188 for hex head bolts again depending upon diameter.

So actually the hex head bolt will have a higher head height and may be considered slightly larger but requires the same wrench for installation. Tolerances are less on the hex head cap screws. Similarly, the width across flats for both heavy hex screws and heavy hex bolts is 1.500 D plus 0.125 and the head heights are the same as indicated above for hex head screws and bolts, respectively.

Since a hex head cap screw may always be substituted for a hex head bolt but not vice versa, the design engineer should select the hex head cap screw. Even with more precise tolerances, the higher quality hex cap screw may be less expensive as most manufacturers are standardizing on the cap screw configurations. For higher strength steels, the heavy hex configuration is recommended, while for CRES and most non-ferrous applications the regular hex configuration is usually more readily available. (Source for Dimensions: ASME B18.2.1 Square and Hex Bolts and Screws)