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 Post subject: Re: Chassis material?
PostPosted: 19 Dec 2009, 22:43 
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Joined: 13 Jul 2009, 20:01
Posts: 92
Location: Space Coast Florida
msmpe wrote:
One nice thing about using a thick frame plate is you can tap the holes in the plate and screw direct to the plate so you can eliminate nuts on the other side. Wow - that'll make life easier! :D Make sure you use lock washers, use coarse threads, although in #6 and #8's I don't remember if there are coarse or fine. Also your tolerance in layout will have to be closer as you will lose the "slop" for misalignment that you get with an oversized thru hole (actually two holes - the hole in the plate and the hole in the component). A trick I use for all my layout work is to draft the plate hole layout in CAD (I use AutoCAD, but TurboCAD is free), then just superimpose a full size print on the frame plate and center punch thru the drawing. It increased my layout accuracy by at least an order of magnitude. Using the mirror plate I might also suggest doing your layout on the underside (reverse the print), drill each hole with a pilot hole from the underside, then finish drill from the mirror side. The idea is to protect that finish as much as possible. But you have plenty to practice with. Keep your tap holes smaller than the book spec rather than larger/oversize and let the tap bring it to size. That way you will have the full strength of the thread(s).

I would stick with the recommended drill sizes for tapped holes in aluminum. Do not use the Titanium coated drills and taps, the aluminum sticks to the coating. Bright finish high-speed steel drills without any coatings are best for aluminum. Aluminum may be a soft metal, but can be a bear to tap if the holes are undersized and the smaller size taps can easily break. I have found that using a high quality tap (i.e., Greenlee, etc.) produces superior results and far less binding when tapping. The taps you buy at Ace, Lowe's, Home Depot, etc. are horrible. They snap and the threads they produce are very poor. The taps are not sharp and the surface tends to bind to the material you are tapping. 1/4" thick threads will give you a lot of holding power. WD-40 works well for a thread tapping lubricant if you don't have something like LPS #1 Gold cutting fluid.

Lastly, if you do not like tapping aluminum you can buy press in threaded inserts and studs at McMaster-Carr or some other supplier.

I tend to prefer thread lock (i.e., LockTite) to lock washers.

Since the free-bee 1/4" plate is no longer available, 1/16" or even 1/8" plate is more than enough for a chassis.

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