1.75" female threads on blind hole?

[BigDave]

Ok, so I am going to take a block of 7075 aluminum and bore 2 holes about 6" apart. Then the openings need to be female threaded to accept threaded male gland nuts to hold stuff in.

How does one make such large threads into tehe openings of holes> I know I can use a four jaw chuck and offset each hole till it indicates on center and then thread it internally with a boring bar with a thread insert, but is there a way to do it on a vertical mill?

It seems UNC or UNF taps that size are next to impossible to come by and make be really expensive if they did make them.

[bdarin]

Big...2 choices: 1-the lathe method, which you already know; or 2-make a tap. Thread some steel, cut some lengthwise grooves. Since you're cutting into aluminum the tap won't need hardening unless you're going to use it a lot.

[halfnut]

You are on right track. You could use toolmakers buttons to establish hole locations. I cheat, stick on mill, use DRO, and then make some kind of accurate hole I can indicate in on when I move to 4 jaw chuck.

Some times I spot drill, then bore-ream with endmill. Example 7/16 drill followed with a 1/2 endmill, not reamer, the endmill is stiff, holds location, and makes a good enough surface to run an indicator on.

Good luck

[Ron LaDow]

Halfnut,
That's not cheating; that's using what you have...

[C. Tate]

I hate cutting threads in a blind hole. My method is to find someone in the shop and bet him ten bucks he can't do it. It's worth the money.

[SGW]

Set up a dial indicator on the lathe carriage so you know when to disengage the halfnuts. If you run in slowest backgear, you can stop the carriage within a thou or two of the same place every time, even with a fairly coarse thread.

Or run the lathe in reverse and thread it coming out. You'll have to put in enough of a runout groove in the bottom of the hole to start the threading tool in.

[Thrud]

Dave;
Yes, it can be done in a vertical mill if it is CNC and has spiral interptation for milling threads (works great). Call around to some new machinery dealers that sell Haas or Okuma CNC mills and ask for a "demo". If you are nice to them, they may do it for you for free - but I would not count on it.

If you have to do it the hard way, you might be able to get a tap from KBC. Making your own tap for two holes is not a bad idea but use lots of lube when you tap it. A-9 works well. If you can chuck it safely and thread it in the lathe do it.

Have fun
Dave Smith

[BigDave]

There has to be somebody that makes taps larger than 1.5".....I am not into making everything though...

I have seen helical interpolation prgrams for CNC, but it is a regular vertical mill, and I am the numerical control, http://bbs.homeshopmachinist.net//wink.gif

I just got both the lathe and mill delivered today. The knuckleheads put the aluminum angle extrusion upside down so the too short end only covers half of the encoder rod for the carriage feed readout axis.

On the mill they extended the table encoder rod so far that one cannot screw in the male taper pipe thread x hose barb fitting drain tap for the coolant hoses.
Oh well, I guess they will have a lot of correcting to do....

[artificer in metal]

Special order is a wonderful thing. I've seen as big as 2 7/8" pipe taps (probably bigger available if you want!!). On a mill a boring head is what you would use for threading but these are not cheap either. Mind you with even a bottoming tap the bottom 2 threads or so aren't much use so for a shallow connection you may have an interesting time. You may wish to look at a banjo style connection. This is used on a lot of European machinery. I am not sure on details but I can give you what I know if you are interested.

[Ron LaDow]

C. Tate,
Very good idea, combining machining with psychology...

[halfnut]

Dave,

Wholesale Tool has taps up to 4", 1 7/8 taps in my 1997 catalog going for about 70-80 bucks, overstocks are cheaper. I have managed to get off their mailing list. Enco is failful, every month they send me a sale flyer of some such, haven't bought anything from them for a year.

I have had really good luck with Wholesale Tool in the past, service is fast, next day for me if I call before 1pm. Quality is sometimes iffy, they will take it back if you aren't happy. More shipping charges, but the next one will be better.

[GregR]

I just looked in the J&L catalog on page 203 of the 2001 catalog. Here are the hand taps they show for 1.75":

1.75 - 5,6,8,10,12,16,18, and 20 They are each priced at $89. The dies are on page 258 for the same sizes and cost $69.

In the Travers 1999 catalog on page pg 203 (wow the same page as J&L)

1.75" taps with pitches of 5,6,8,10,12,14,16,18,20,24,and 32 costing from $82 to $71. The dies are on page 214 in the same sizes costing $51.

You can get these large sizes if you can live with the $$$.


Hope this helps.

Greg

[farmwrench@aol]

I vote for makeing the tap. This is going to be a gland fitting... right? so it souldn't be under an outragous amount of pressure and shouldent be removed or even tightened more than once every year or so if that and you don't have to worry about the hole having anything but that follower giong into it and you have to set up to make the follower for the packing any way. Just make a threaded shaft or three (if you want to be fancy about the bottoming progression. I made a double ended one with a hole in the middle for a 3/8 rod as a tap handle) and cut some flutes they dont have to be real big although it helps if you have less thread friction and for chip clearance. I didn't index the flutes or square the head but it only had to do one hole. Just put a hole in the side to stick in a shaft through to make a tap wrench and go to town.

[SGW]

FWIW, I've always found Travers' "generic" house brand taps to be pretty good quality, and they do seem to be a little cheaper than some other places.

For one hole though, I'd thread it in the lathe. It's not as though you're working on an irreplacable casting. You can afford to have a couple of "learning experiences" and still come out ahead vs. paying $80 for a tap. And when you succeed in doing it, you'll feel good...and know how to do it next time.

Even with a tap, with something that size you'll have to cut at least part of the thread depth in the lathe, anyway, unless you've got one honkin' big tap wrench and a Gibraltar vise to hold the piece in.

[This message has been edited by SGW (edited 08-11-2001).]

[BigDave]

Yes, it is a gland nut to retain a hydraulic piston rod. Rather than using 2 side by side cylinders and connecting them with cross pieces, instead a block of alumium is machined with two holes to act as the female rod receivers.

These other catalogs eveveryone is mentioning, can you provide a web address or tel #?

Thanks guys.

[C. Tate]

FYI Widell Industries will make what ever you want. They made a 1-7 doudle lead tap for me. You ought to go to their site just to see the big tap. widell.com

[GregR]

Web addresses:

Travers: http://www.travers.com


J&L: http://www.jlindustrial.com