drill/tap 1/2-13 on machine table

[kkominiarek]

We have a machine here that has a 30" x 60" table on it but only has 3 t-slots for clamps. We are going to drill/tap 1/2-13 holes on it....probably in a 2 x 2 pattern.

 

Any tips,tricks or best practices to help me avoid breaking a tap or drill off?

 

What is a machine table normally made from?

[DaveR]

Holy cow.

 

 

Don't machine your table, just make a sub plate. Nice 1.5" thick piece of Blanchard gound steel or even aluminum will get the job done.

[crazy^millman]

Yeah I would never do that in a million years. Sub plate all the way.

[ROB]

[bozzy2]

The table could be made of plain carbon steel, alloy steel(4130 or 4140) or could be menite(cast steel). When I worked at Texas Isturments, we put a 30" X 60" x 3" aluminum riser onto the table and drilled and tapped the riser. I would hesitate drilling into the table of your machine. The aluminum riser can be machined into, you can add new hloes at any time, and the table can be resurfaced many times before it is used up.

[Tom Szelag]

Ooooh, don't drill into the table.

 

As has been said, thick plate of Aluminum sub plate will do the job well. Bolt it on and leave it on.

 

We have two or three sets of 1/2-13 holes drilled and tapped for vises and our 4th axis, and then a 1x1 grid of 1/4-20.

 

Hasn't corroded in 6 years of continuous use. Easy to drill and tap, easy to resurface with a fly cutter if it gets some muck on it or you dig into it a little bit.

[GVM]

If your planning on any fixturing you might want to look at a subplate from Stevens Engineering www.stevenseng.com

[Chris Rizzo]

What they all said. I prefer to thread mill my holes in fixture plates, there is no tap to break then!

[kkominiarek]

Sub-plates have been discussed for this machine.

 

One of the negatives to a sub-plate (for this machine) is that we do some tall work on the machine. Losing 2-3" would hurt us in that area.

 

We may have to go both ways, sub-plate as well as tapped holes in table.

 

Maybe instead of a 2 x 2 pattern we can enlarge the spacing or drill & tap holes specific to fit certain parts.

 

We aren't drilling any table yet we want to make the right decision.

 

Thanks for the answers....keep them coming

[Trevor Bailey]

Drilling into your table is no big deal. I ahve done it plenty of times. Here is why: I have bored holes in the backs of my vise/fixtures and inserted hardened bushings for 1/2" dowells. I did the same thing for my table. By doing this, there is never a need to indicate a vise of fixture in. Think if you have 5 vises to set up for a job. Would you rather indicate each one in or just set them down on dowel pins. You will also gain yourself the 1.5 to 2" extra travel in Z by not having to add a sub-plate. Most will say that is not neccessay, but most dont use right angle attachments either.

 

Now on the flip side, I would prefer to use a sub plate, because of all the different benefits of having it. Too many to list. Just wanted to let you know that drilling into and tapping the table is OK. I would hand tap though.

 

Think about this.....what if you decide to sell the machine one day and get another one. I know that if I was in the market to buy and saw a table with a bunch of holes in it, I would turn around and walk away from it.

 

Just my .02$

[iowajim62]

Another thought on supbplates.

 

Mount it on risers that are keyed/bushed to the table/fixture and then drill your holes thru.

This allows coolant/chips to fall thru. And the best part is you'll never ever have to hold a rag over the holes to clean them out.

 

Also, have you ever seen the table after a subplate has been on a few/many years ? Yuk !

[Matt Berube at Ferron Mold]

My subplate opinion is 1.25 thick aluminum and use a spiral flute tap. Then you can go like hell and not break anything. Also, BEFORE you start machining any jobs (immediately after tapping)put a set screw in each hole to keep the chips from packing them solid. It's a lot easier to clean out a hex socket than a 1.125 dp hole. It's a nuisance but it's well worth the effort. There are 1100 1/2-13 holes on the subplate for our newest machine.

[Tom Szelag]

+1 to plugging your holes. Something we havent done...and its a pain to go back with a dental pick and clean the things out.

[Paul McGarr]

If I could hold back, I wouldn't comment. Dude, don't drill into your table. I can see a hole or two, but to emulate the convienience of a subtable without a subtable is a BAD idea.

 

Take any piece of precision ground stock (especially 30 x 60 inches) and poke a few hundred holes in it. It is no longer flat stock. I don't care what it's made of...and we're not talking tenths.

 

Paul

[tlameto]

We have dowel pin holes in the table and use various subplates. Depends on the job. The subplates locate on the dowel pins, so the repeatability is there. Set screws in the holes is the only way to go.

[jeff]

The main reason that you would NOT want to drill into your table is if you were to sell that machine one day.

I doubt anyone would buy it with a bunch of holes in the tbl.

If you can get away with a short enough riser, that would be best.

[Chris Rizzo]

You don't have to loose alot of Z with a sub-plate. I've got one that started as a 36 x 20 x 1" plate of A36, and by the time it was ground and stress-releived turned out about .950 thick. That's why I chose steel instead of alumin., so I could use a thinner plate and still have decent strength of threads. Bore holes and thread mill and you easily get .800 of thread depth. I'm a fan of steel subs, then again I've got fixtures going on and off 10-15 times a day. I also know that someday my sub will eventually need to be replaced from the constant on/off and running bolts in and out all day....and that's alot cheaper than replacing a table.

[Tim Johnson]

I agree with the 1" steel plate. I think Advent has an indexable thread mill that would do the job. Use plastic set screws for your plugs. The odds are pretty good some of those screws will be in for quite a while.

[cblythe3d]

If you drill your table your grid will be a mess

t slots interfering at odd spacing with the grid.

Making a sub plate with 1/2-13 holes thru at absolute machine position positions and .501 bores 1/4 deep for each hole provides best of both worlds. While the hardened bushings are first class the bored locating holes will suffice to accuratly locate work for years.

 

I use a 2 inch grid for 1/2-13 and plug the holes with plastic caps eliminating cleaning problems.

 

Charlie

 

Added bonus if you sell the machine

[CAM-mando]

I agree with the 1" Subplate.

 

You can mill a keyway down the length and put keys on your mill vices for quick setups and the flexibility to locate them anywhere on the table.

[BIG DOG]

I have a sub plate that covers all of the table, we have a lot of ½ taped holes in the center of the plate at a set pattern around .75 wide key slots and alternate with 5/8 and ½ taped holes near the outside of the plate. The plate is 2” thick 28” in Y and 70” in X. Its a lot of work to tap 2000 holes, and a lot of work keeping set screws in the holes we are not using, but I can locate off any of the key slots for program zero ( 7 cross keys ), and can bolt any thing to the table, anyplace.

Now if I can only get the designers to use the bolt pattern, any suggestions

[mcpgmr]

Subplate all the way. I don't like keying things either if I don't have to. I'd rather see the fixture or vise move a little and scrap a part rather then transfer all the energy from a crash in to the spindle. JMO !

[wildcat99]

For our router we had the factory thread holes 6-in on center in our twin 5x5 aluminum tables before it shipped. They did this with the machine, but I don't know what type of tap or drill. This works out to be 100 holes in each table for fixturing.

 

After the machine was set up we surfaced the table with a fly cutter and threaded steel inserts into the holes. Works great!

 

2 or 3-in of lost clearance would have caused us a major problem also.

 

HTH