View Full Version : Need Help
05-01-2004, 6:55 PM
I'm in the process of building a mobile base for my PM3520A lathe. I've got somebody to do the welding. My job is to drill the 4 holes in the u-channel (3/16" thick), to bolt onto the feet of the 3520.
1) What would be the best type drill bit to use?
2) I need your fool proof ways to layout the holes in order for them to line up with the holes in the lathes feet after all is done? In order for my face not to look like this... :o
3) Oh, and would you drill the holes before the stretchers are welded to the u-channel, or afterward? I think it would be easier for me to drill afterward, so as to get the holes in the correct location, but it would be heavier to try to drill on the drillpress. So that's why I'm counting on your ideas! Thanks,
05-01-2004, 7:12 PM
W.C., I would use a typical drill, either 118° or 135°. I'm not a machinist, therefore I don't know any better, therefore I would grab the first one that looked sharp!
I have observed that drilling a small hole first, started with a prick-punch, makes the bigger hole go faster. Start with a 1/8" bit, then use the full sized (3/8" or 1/2" or whatever it is) drill. 1/8" bits are cheap - get a couple. Using cutting fluid will extend the life, but I'm not sure what to recommend there.
You can make a wooden template (1/4" plywood) to test your pattern. When trying to measure hole distances, remember that the distance from CENTER to CENTER of two round holes is the same distance as SIDE OF HOLE to SIDE OF HOLE. Eyeballing the side of a hole is easier to see and measure than a guessed center. Oversize holes or elongated holes are fine, just not too big. A hole can be elongated with a round file, or a jigsaw.
05-01-2004, 7:17 PM
WC, one thing to consider is the way that the base will affect your feet when using the lathe. You'll want the "front" rail offset if at all possible so you can get close to the lathe. Or use a design with just one beefy rail down the middle.
05-01-2004, 7:52 PM
It sounds like you've thought out the difficulties. If the welding alignment is not perfect, as mine would not be :o , things might change if you drill the holes perfectly before weldup. I would definitely do them on the DP vs hand drill if at all possible. Even center punched the hand drill will try to walk. Also, the drill will try to grab. Neither of these are too much problem on the DP. Oh, and set it at the lowest speed. Any cutting oil should work as a coolant for the bit. I have drilled holes like this with a hand drill, it is just more work.
Todd and Jim's advice are both good. Unless there is a real need, I would drill the hole slightly oversize too to allow for a little misalignment.
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