Brian builds a Corliss

[Ghosty]

Brian,
I was going to suggest that you get some more taps and dies and use plenty of lube on them. Work out how many holes and divide by the number of taps and only do that many holes and then use a new tap. And just take it slow, what you don't get done today, you can always do it tomorrow.
Still following along.
Cheers
Andrew

 

[Brian Rupnow]

Thanks Andy.---I just had my tap drill size confirmed by someone who taps a lot of steel with #4-40 taps.---Brian

 

[Brian Rupnow]

Today was one of those seriously bad "Everything I done turned to poop" kind of days. I managed to drill four holes (well, actually only two show) holes in the wrong place and managed to break a #4 tap and a #5 tap off. I did manage to get everything I have made so far mounted to the baseplate. i don't have days like this very often, but man, when I do I really do!!!

 

[Ghosty]

I just had my tap drill size confirmed by someone who taps a lot of steel with #4-40 taps.---Brian

Brian,
From the Engineers Black Book, the 4-40 drill size is a #43, which gives a 71% thread depth. Just thought it may help.
Cheers
Andrew

 

[Brian Rupnow]

A #43 drill is 0.084". My machinery handbook tells me that I can safely go to a 0.095" pilot drill in steel. and Chris confirms that drill size is what he uses for #4 cap screws. I'm terrified of breaking taps in the cylinder, so will probably go with the 0.095" diameter drill.---Thanks--Brian

 

[Iampappabear]

Brian, try to get a Blue Wizard tap and use decent tapping fluid you should be fine.

Recommended tap drill sizes are based on the thread depth of a standard full nut (the diameter of the bolt) if you are going deeper, you can cheat a little by going oversize with the tapping drill.

Colin

 

[Steamchick]

I am a well practiced tap-breaker... 6 BA and smaller. Somehow everything is fine then my body twitches and "hey presto!". The tap has broken.
But slightly oversized tapping drills can help.
Brian, How do you clear the broken bits?
K2

 

[Brian Rupnow]

Steamchick--I use a center cutting carbide end mill the same diameter as the tap drill to remove the broken tap.--OR --I use a larger endmill, cut a larger hole which includes the tap, mill to depth or all the way thru, then ream the hole and Loctite in an aluminum plug, then start over.

 

[Brian Rupnow]

Today I picked up my shoulder bolts from my friend who can still order thru McMaster-Carr. They look tiny, and they are, but they should do the job just fine. I also picked up a 2 1/2" square piece of A36 mild steel x 2 5/8" long, and milled it down to 2 1/8" square. I don't get a really spectacular finishes from my face mill, and I guess it must be time to turn the carbides to present another face to the work. I left the material a bit over length, because I get really good finishes with my lathe, and the cylinder has to be set up in the four jaw chuck to drill and bore the 1 1/8" thru hole, so I will finish it to length in the lathe.

 

[Steamchick]

Thanks Brian. As I usually only have tool steel small taps I should be able to manage that. Just have to buy the carbide end mills in the appropriate sizes.
I have broken the odd small centre drill trying to drill-out a tap. Biggest problem is the small size.
Thanks for the advice!
K2

 

[almega]

Just curious. How do you align the tap with the drilled hole when tapping? The threading table I have indicates for a #4-40 thread a #43 drill should be used for aluminum and a #41 for steel with 75% and 50% thread engagements respectively. In aluminum I generally go with a #42. If you are having a tap breakage issue, you could go up to a #40 drill but you would want to be careful when tightening the shoulder bolts so as not to over torque and strip them.

 

[Brian Rupnow]

I normally don't use any kind of tap guide. However, for this cylinder, I will fabricate a tap guide that fits in my milling machine.

 

[almega]

Since I started guiding my taps I have broken very few taps, even small #2s. I generally set up in my mill and drill all of the holes and then go back to the same coordinates for each hole to tap. I have a 3/8" diameter "guide bit" made in the lathe with a 90 degree included angle point that I put into a 3/8 collet and line up to the hole in the tap wrench handle. I then lightly drop the quill as I turn the tap to keep everything straight. This keeps everything in perfect alignment and doesn't take that much time, especially when compared to fixing where taps are broken. Nothing too complicated and no extra gizmo to find a space for. If you have a DRO it is easy to find the coordinates for each hole.

 

[Gordon]

As others have said, buy or build a tapping stand. It makes a lot of difference. Keeps the tap straight and gives a much better feel for how much torque you are exerting and lets you feel when the tap bottoms out.

 

[Vietti]

I have a piloted tap wrench. The pilot,+/- 1/8", fits in the drill chuck. Tap the the newly drilled hole after drilling the hole and don't move the table. Works very well, is balanced nicely and does taps up to #10 size taps. Highly recommended.

 

[Brian Rupnow]

Today I'm really starting to miss my lathe. I'm at the point where almost everything I have left to do requires some lathe work. I have been looking up info on how to tap holes without breaking a tap. This one as described in a video by Joe Pi comes highly recommended, and should be used with a spring loaded tap driver in the mill spindle.

 

[Jasonb]

That's a bit fancy. I just have a short length of 1/4" drill rod with apoint at one end and a ctr drilled hole at the other so it suits small taps with no hole in the end or ones with a ctr hole. Hold that in the collet or drill chuck and use the quill to bring it down onto the end of the tap, tap wrench on the taps shank. Can't remember when I last broke a tap. DRO positions quill directly over the hole as mentioned a couple of posts above.

 

[rhitee93]

Sorry to burst in after not posting in years, but I use one of these, and love it. The pilot on the back fits in a collet or drill chuck in the mill to maintain alignment. However, being a small tap handle, it gives great feedback. They are cheep too.

https://www.mscdirect.com/product/details/05041850

 

[Vietti]

That's what I'm talking about! Some T handle wrenches like this have hole in the top so a pilot is easily added. Check yours. I wouldn't say I've never broken a tap with this tool but I do much better than with other tapping schemes.

A small pilot is nice for most smaller taps so you don't have to open the chuck so far to insert a 1/4" pilot. Just grip the pilot loose enough to turn it easily and advance the quill if needed for a deep hole. On withdrawing the the tap you may need to grip the key less chuck so it doesn't tighten on the pilot as you turn the wrench to withdraw the tap.

 

[almega]

Tapping stands are nice but you still have to get the hole properly aligned with the tap to be perfectly vertical and you have to have a place to store it. I only have one little bit to store and I know on my mill that I have the hole perfectly aligned each time. Here are a couple photos: one of the bit and the other of the set-up. BTW, that happens to be a 4-40 tap.