What do you think of this build video? Did he take a big risk?

[shild]

Was watching this build video comparing what he did to what I would have done for these 2 frame rails. He did all the holes one after another with the finished sized bit. I would have started with a center drill, then intermediate drill, then finish size on each hole before moving table for next hole. Guess since he uses a transfer punch for the next stage, it doesn't matter if they're not so accurate so I would have changed a lot of bits for nothing?... But look at what he does at 12:27 using a hand held drill to tap with. Didn't go backwards until hole was completely tapped. Wasn't that a huge risk? What do you do if you snap your tap off flush in the hole? Guess he would have to grind away that part of the frame and fill it with weld and re-do hole? Or start over? https://www.youtube.com/watch?v=rAXgvtK ... 5h&index=2

[AnthonyDuarte]

Considering the obvious runnout on the drill, the holes probably should have been spotted first. An intermediate drill on something this diameter is not necessary unless size is absolutely critical, in which case finish it with a reamer or bore it. On that part of the frame, those are just bolt clearance holes. With enough hole clearance between all the mating components, it's a surmountable error later on in assembly.

As for doing all operations before moving the table, that's not really necessary if you always approach the hole location from the same direction, or if you have a DRO that reads off the actual table position. The value of doing this is really situational. Very few situations where the extra time changing tools is worth it.

As for the tap, I don't think think that's a hand drill. That looks to be one of those tapping arms, so the tap will always start square. If he sized his holes right and it's the correct tap for the material, it won't break as long as he's cautious going in (which he is). Looks like a tap with a generous lead too, so there's not much worry about. Can always chase it with a bottoming tap later.

[Harold_V]

I was trained in a facility in which a guided missile was the product. Work began with the R&D phase and continued through the production stage, where drill fixtures were available for drilling of most holes. With drill fixtures, slip renewable bushings were provided for holes that required greater precision than a drill could provide (one could drill, then ream the hole).

During the R&D phase, pretty much all holes were drilled without the use of fixtures. Some, with broad tolerance, were even drilled on drill presses (the shop was equipped with several six spindle gang drills), but anything with tight tolerance was drilled on drop spindle mills (think Bridgeport, although there were none in the shop. Most of the mills were Gorton). We were required to double drill, with all holes started with center drills (in my 7½ years of employment there, I never once saw a starter drill), with the hole generated by an undersized drill, then opened to size with the designated drill size.

Here's the deal. As Anthony stated, unless there's good reason, a hole, in general, can be drilled without double drilling. However, if you have the least bit of concern about the outcome of the hole, that may not be a good idea. That's especially true if you sharpen your own drills, and aren't adept at getting the grind uniform, both in angle and length of the lip. A drill that is not perfectly centered will wing on the web, creating an oversized hole. The hole may start out well oversized and slowly get reduced in diameter, but that condition isn't exactly good, either. For that reason, starting a hole with an undersized drill often ensures that the desired hole comes out on size. The created hole eliminates contact of the web of the drill used to size the hole, so even if the drill may not be properly ground, it will seek center and drill on size, as the margins of twist drills are circular ground and are not intended to cut, but only to pilot the drill.

If one hopes to be perceived as skilled at machining, there's a few things that can be done to elevate one's workmanship above that of the average ham handed individual. One of them is to spot drill locations with either a center drill or a spot drill. Both work perfectly well, in spite of the protestations of those who think only a spot drill works. The other is to double drill holes, even when they may not be critical. What that does for you is to guarantee a good hole.

The choice is yours. There is no mandate to follow these guidelines.

H

[Miserlou57]

Did anyone else pucker at 9:30?

[ChuckHackett-844]

Tapping: The video isn't clear enough for me to see the shape of the tap. I regularly tap with a hand drill if not tapping very deep (which he didn't) and the hole is through or at least overly deep to catch chips. I use "spiral point" ("gun tap") taps whenever possible - they are great! ... even 6-32.

They are not designed to be repeatedly reversed like a 'normal' tap (and it's dangerous to do so with them). Since they push the chip ahead of themselves, the hole needs to be a through hole or deep enough to hold all the chips.

There is also another type of tap that has flutes like a twist drill (can't recall the name) where the chip comes out of the hole as with a twist drill. This tap too can be easily used with a hand drill.

[FKreider]

Did anyone else pucker at 9:30?

Yeah, gloved hand by a spinning cutter is a very bad habit to get into. Other than that I did not see anything wrong in this video, these guys are professionals who do this work every day. As Anthonly stated the tapping looks to be done with a "flexarm" tapping machine which is designed for this exact purpose.

[shild]

Thanks for the replies guys! Anthony I didn't know that was a tapping arm. That explains it. Since I don't have one, I guess I'll have to tap with my mill/drill. You really think I won't have problems if I move onto the next hole with same drill instead of locking table at each hole until completely drilled and tapped huh? Harold, thanks for letting me know I don't need an intermediate bit. Chuck, I didn't know about those other taps. Fkreider, I can't put my finger on just why, but yes it does look professional like he is doing all the mandatory stuff but not doing anything he doesn't have to do like excessive de-burring as I might have done. I guess I'm learning a lot from this video. But being that it's supposed to be professional I wonder why it's not nearly done yet?

[shild]

These guys really seem to know just when to stop working on a part and move on to the next one. Not sure why the Loco isn't nearly done yet. Does anyone know of other build videos as good as this?

[steamingon]

Have you seen this build; https://www.youtube.com/watch?v=tdBjm5D6jxY

[Sandiapaul]

That flex arm tapper is a great thing. We have one at work. I tapped over 400 holes in 304 SS with one tap. A 2-56 at that.

[shild]

Have you seen this build; https://www.youtube.com/watch?v=tdBjm5D6jxY

No I haven't, thanks for the link, watching it now. Looks like a simple chassis but especially difficult boiler. Isn't it?

[shild]

That flex arm tapper is a great thing. We have one at work. I tapped over 400 holes in 304 SS with one tap. A 2-56 at that.

I see. Probably isn't worth having unless you're doing some serious tapping I guess?