Cutting Threads in Carbon Steel

admin

I have a 1566 carbon steel shaft that I want to drill a 3/16 (or maybe 1/4) deep hole to have a set screw (from a sprocket rest in). However, I don't just want a hole, I would like a tapped hole that the set screw could thread into. The set screw I have is a 1/4 - 20 x 5/16 and I of course am buying a 1/4-20 hardened steel tap. This may sound dumb, but I have never tapped anything before. Do I drill a hole slightly smaller than the tap (say a 3/16 in diameter if I need 1/4 inch) or do I just drill it to 1/4?Last edited by GoK4rtFanatic; 15 Hours Ago at 12:06 PM.Century FC-90Primeweld TIG 200D
Reply:#7 drill bit for 1/4-20.
Reply:Also, there's tap drill charts online that are helpful for the most common tap sizes. Just make sure that the chart is labeled for the type of tap you're using, be it cut, roll form, STI, etc. Sent from my SM-F711U1 using Tapatalk
Reply:Use the correct size drill bit for both holes.How tall is the sprocket and how close to the set screw hole are the teeth? If the sprocket is too tall, you may not be able to use a typical tap wrench.When you screw the tap into the sprocket, that is the easy part. Do that first. If you are also going to thread the set screw location, you will need to make sure the sprocket does not move. You also need a bottoming tap. Here are two different tap wrenches. You might need the bottom style.

Sent from my SM-G996U using TapatalkMillermatic 252 MIGMiller Dynasty 200DX TIGMiller Spectrum 625 PlasmaAltas 12x36 Metal LatheBridgeport Milling Machinewww.psacustomcreations.com
Reply:Everything you ever wanted to know on the subject:Miller Multimatic 255
Reply:I will watch the video as soon as I can, but is a bottom tap really necessary? I only need a few threads and it will have enough to tighten down on. As for the sprocket diameter, I am almost 100% sure the tap is long enough to not bump the sprocket teeth, as the sprocket is only 2 1/2 in diameter, so it would only need to be approx. 1 3/4 inches long to tap a 1/4 inch hole. How big of an issue is it if I don't use a bottom tap? I was planning to just leave maybe that last 1/16 in at the bottom untapped.Century FC-90Primeweld TIG 200D
Reply:You only need a bottom tap on a blind hole. Set screws are not usually in blind holes. Can you confirm?Miller Multimatic 255
Reply:Get a tap that's HSS, a spiral point tap.Don't buy a tap from a bigx box hardware store, they are all garbage.Go to a real industrial supplier.
Reply:

Originally Posted by 12345678910

Get a tap that's HSS, a spiral point tap.Don't buy a tap from a bigx box hardware store, they are all garbage.Go to a real industrial supplier.
Reply:Yes, I know the hardware stuff is garbage. I just bought a hardened steel tap from McMaster carr. I did not know I needed a bottom tap (had no idea there was a difference). It is a blind hole unfortunately, however I am still rather confused on the issue with it not being fully threaded. Obviously I will purchase a bottom tap if necessary as it’s handy to have but what changes if I am missing maybe 2-3 threads at the bottom?. In my case, the hole I drill doesn’t even need to be tapped (I am just doing it for a flush fit). If I take a set screw with a length of 5/16 in and drill a hole that is 1/4 inch deep into my rotary shaft, and the tap threads 3/16 of that 1/4, what problems arise? Loosening? Improper thread connections? I’m cheap so I like to be absolutely sure I need something (which it sounds like it does, I’m just trying to understand why).Yes I probably should have just bought a tap set but they are expensiveCentury FC-90Primeweld TIG 200D
Reply:Look at the end of these taps.This shows how the end of a taper tap does not have much in the way of cutting.It will touch the bottom of the hole before it makes threads. Even a bottom tap has a partial thread for the first small portion.If you do not need it threaded, just make the shallow recess the end of the set screw goes into.

Sent from my SM-G996U using TapatalkMillermatic 252 MIGMiller Dynasty 200DX TIGMiller Spectrum 625 PlasmaAltas 12x36 Metal LatheBridgeport Milling Machinewww.psacustomcreations.com
Reply:This is the tap I bought so I guess I’ll be ordering a bottoming tap as well.

Century FC-90Primeweld TIG 200D
Reply:OP, I don't think your going to get your desired result running a set screw into a threaded hole in both the hub and axle shaft. Nothing will tighten up to hold the hub except the shear strength of the screw which will probably lead to the holes wallowing out and the screw falling out. I drill divots in the shaft and tighten the set screw, tap the set screw and tighten it again, that sets the tip of the screw into the shaft steel.  To illustrate what I'm saying take 2 nuts on a bolt and turn them at the same time... they will never tighten unless they are turn against each other.
Reply:If you are planning to go through threads in the pulley and then on into the threads in the shaft too then you are going to have to index them by starting the tap while threading it through the hub until you get first few threads started.As mentioned this sounds like a poor idea as it can't tight up the assembly. Make a hole for the tip then run a second setscrew down on top of it so it can not back out and your golden.
Reply:I am not a good enough artist to draw out my plan, however I can try to explain with more pictures. Essentially, I have a 3/4 inch carbon steel rotary shaft (figure 1). I have ordered rotary [shaft] sprockets (figure 2) from McMaster carr that have two set screws built in to be tightened against the surface of a rotary shaft (for some applications this would be enough, not for mine). I intend to tap a 3/16-1/4 deep hole (with 1/4-20 threads (matching that of the set screws)). The set screws (yes plural, there are two), could then be run through the OM factory tapped holes in the sprocket and into the tapped holes in the rotary shaft. If this were the case, no “jam set screw” is needed, as it is tightened like a bolt into a threaded hole.

Figure 1

Figure 2

Century FC-90Primeweld TIG 200D
Reply:Your overthinking it, if you want drill a divot hole in the shaft thats fine, but dont go too deep maybe an 1/8” or the tip of the set screw will smush over and you will not be able to back it out. One thing i have done when using set screws in areas that have a tendancy to come loose is tighten the first one up and lock the firtst on down with a scecod set screw. Im guesing your not planning on having a keyway in the shaft? But 2 little set pockets for the set screws and thats not ging anywher unless serious horsepowerDo not argue with an idiot. He will drag you down to his level and beat you with experience.
Reply:Oh ok, I see now. Yeah I have tried the key ways before and was not satisfied with their results. Is it still worth while to tap the 1/8 holes you recommended I drill? I would like to ideally but it really is not necessary.Century FC-90Primeweld TIG 200D
Reply:Sprocket without a key is crazy.
Reply:If you're experiencing the sprocket coming loose, use a gib key.
Reply:For drilling/tapping on a shaft, I grind a flat spot on shaft perpendicular to the drill bit first. As mentioned tho, trying to tap sprocket and shaft together is difficult. You could drill separately and tap together but why.
Reply:If you don't have a machine shop.........you might consider drilling the sprocket, and shaft, in one setup..........then using a bolt as a shear bolt.  Drill the thing all the way through sprocket and shaft, then insert bolt.