advice on layout and drilling holes needed

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So, here at the shop we are looking to build a welding layout table. The design is looking at being a 5'x20' over all size by 36" tall, 3/4" or 1" thick top on a beefy frame. In order to facilitate clamping we are looking at a 6" grid of 3/4" holes with nuts tacked underneath.My waterjet guy is advising me against having all those holes waterjetted, because of the material thickness / time for the waterjet to piece all those holes. I am however getting him to cut the tops (4'x5' pcs, 5 needed to make overall top) to the right size so this thing will be square.So I am looking at having my shop fabricators drill all these holes. I will be using a waterjeted layout jig to transfer punch all the hole locations, but does anybody have any suggestions on how to line up the mag drill with an annular cutter over the hole location after I have transfer punched it? I could always change out the cutter with a drill chuck, use a center finder to make sure I was lined up, replce the annular cutter, and drill, but that sounds like a pain in the ***. And does anybody have an idea what the estimated time to cut a 3/4" hole in 1" thick steel will be? I am looking at 400 holes total. How many holes is the annular cutter (proper technique, speed, and fluid assumed) good for?Thanks in advance for any suggestions and advice.Troy
Reply:The annular cutters that I have used (Hougen) have a spring loaded pilot for centering. I would think the actual dilling time per hole would be relatively fast, around a minute or so per hole.
Reply:just use a mag base drill and a stub length drill..  drill them and countersink both sides. tapping them is whats gonna suck..tackleexperts.comwww.necessityjigs.comhttps://www.facebook.com/groups/mach...dingequipment/
Reply:By welds4d;The annular cutters that I have used (Hougen) have a spring loaded pilot for centering. I would think the actual dilling time per hole would be relatively fast, around a minute or so per hole.
Reply:Originally Posted by brucertapping them is whats gonna suck..
Reply:I would be thinking having the jet cut the holes a cheaper and much easier solution.  I know the jet will cut the holes faster than you paying 1-2 fabricators (even at your cost) to drill 400 3/4" holes through inch plate.  You will still have to pay for the transfer sheet to be setup and cut, why not just have the jet do the holes while its already set up and eliminate that whole step???Mechanical Engineer
Reply:so, the design has changed slightly. now we are using 3/4 plate with 1/2" holes. I checked on price of water jetting, my local dude wanted $7k just to supply the top pieces cut to my size (5 pcs at 4'x5'). Felt I was getting ripped off, so called local metal yard. quote from them was about $2500 for 3/4 x 60 x 240 ( 3000 lbs). so after all the material for the project, including extra forklift rental to help unloading, total project will be about $4000 (including paint, mag drill rental, leveling feet etc).Labour is "free", since it already paid for / in the yearly budget and work is at a standstill in the shop until we get other work in. Guys on a union contract, and I don't want to furlough them right before holidays.pics on way as we build it, hopefully boss approves monies on monday
Reply:I 'am building the same type of table, all be it a modest one at 8x4x5/8".I've been thinking of how to do this the easiest way. The best so far I've come up with is;Clamp bar to longest edge, drill 1st hole then using a milled sq former to the dimensions you require C-2-C less half the distance to the centre of the mag, and the diameter of the hole you are going to drill.Then placing a pin in the 1st hole and butting and clamping the former sq to pin and bar. You can then cut the next hole, etc etc. Once the first row has been drilled place pins in the holes and butt the bar to it, the next lot of holes can then be drilled. Remembering the former will have to be modified to take into account he Pin dia, and bar.Hopefully at the end, the table will have a sq grid.If that makes sense.Any comments/suggestions
Reply:if you have a mag drill,  drill your holes for your, i guess, 1/2 - 13  bolts and tap them with the magnetic drill.  chuck up the tap, take some crisco and run the tap into it and then run the tap into the hole.  hit reverse and you are done.   i have tapped holes till i've worn out taps.
Reply:i'm sure that crisco suggestion has some of you cracking up.  well before crisco, and before i got heart healthy, i used bacon grease.   definitely a lot cheaper that that tapping fluid the costs a bunch and gives it up to gravity as soon as you apply it to the tap.   that stuff and pvc cleaner,  you waste more than you use.
Reply:So on this tapping suggestion, I have used a hand tap, and always had to back off every 1/4 turn or so to break the chips. With the crisco techniques suggested above, it seems I can just tap in all one go? What type of tap, and is there a special shank for chucking into the drill? How much of a chance is there that I will break a tap?
Reply:there are all kinds of tapping heads, tap adaptors etc for mag drills.  there are all kinds of mag drills also, if you buy or rent a mag drill make sure it has reverse;   some people like to drill, countersink and tap;  some just drill and tap.   although i have never done it i have heard you can use an impact gun to run the tap in.  i might have to try that.   there are different feeds and speeds on mag drills.  some are power feed, some manual, some variable speed, some two speed, some single speed.   some of the single speeds spin at either 450 or 550 rpms.  i have a milwaukee that stays in the shop and a champion rotobrute in my truck.  the milwaukee weights 75 pounds, the champion 27.   the milwaukee has all the features and the price tag to go with them, the champion i bought on ebay, it drills with bits or annular cutters, one speed, no reverse; kind of bare bones but it does the job and   it sure beats trying to position that big milwaukee sideways from a chain to drill a hole.Last edited by fdcmiami; 10-16-2011 at 09:22 AM.
Reply:Looks like you figured it out already, but if you would have spent the money to get 4x5's waterjetted for a table top rather than just getting the metal shop to shear/OFC... Waterjetting all of those holes is not a good choice either, yes its accurate and easy, but its MEGA expensive for all of that pierce time and its not like you need the precision.As for laying them out... get a tape measure, chalk line and a center punch and go to work.  It's really not that hardHave we all gone mad?
Reply:The best taps for this purpose will be spiral point tap. They are designed to push all the chips forward, and in your case out the bottom of the hole. A combo drill and spiral tap will also work well and may save time moving the mag drill around. I second the chalk line grid layout suggestion. I also recommend using real cutting fluid, yes it's expensive and a lot ends up dripping off, but it really works. To minimize drips, put it in a cup and use an acid brush to apply.Ian TannerKawasaki KX450 and many other fine tools
Reply:I second the chalk and chalk line method, I'm most likely saying something you know already but when you mark out go 0 - 6 - 12 etc to avoid accumalative error.
Reply:Originally Posted by Stage HandSo on this tapping suggestion, I have used a hand tap, and always had to back off every 1/4 turn or so to break the chips. With the crisco techniques suggested above, it seems I can just tap in all one go? What type of tap, and is there a special shank for chucking into the drill? How much of a chance is there that I will break a tap?