SAE All-Metal Hot End

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I'm planning on making a Stainless Steel Hot End and of course I'm just going to go to the local hardware store which doesn't really have much in the way of metric stuff. --User:Jgilmore Novemberish, 2010.

So I'm going to be drilling out my stainless bolt with a 1/8" drill bit. Do I need to get a 5/16" bolt or will 1/4" do? When I tap a 1/4-20 hole, I like to use a 13/64" drill bit, which implies that the wall will be 13/64"-1/8"=13-8/64=5/64" or about 1mm wall all the way around, less any eccentricity. Which I think should be enough, even given that I'll be using a drill press instead of a lathe. A 5/16-18 bolt uses a 17/64 tap size, which is 1/16 larger, or about 3.5mm extra, so 1.7 wall thickness under the threads, assuming an exactly centered hole. (which there will be, b/c I'll start the hole on that end.) That should be enough to ream?

if I want to ream it out to give a tapered hole, do I need to get a 5/16" bolt? Nophead's bolt was reamed almost completely out, I don't think I want to get that close, as I need to torque the acorn nut and aluminum heater block onto the end.

Do I need to a tapered hole? Nophead seems to think that tapered holes are just magic, and it's hard to argue with his results, so I'm inclined to say yes, I do need to have a tapered hole for reliable operations.

I suppose that it depends on the slope of the reamer. The reamer I found says 1/8" to 1/2", and the cutting edge is 3 3/4" long. My heater block is 1/2" thick. The depth of thread need for the acorn nut on the end will be greater for a 5/16" nut than a 1/4" one.

The length covered by the nut and heater block will be the molten zone, with the melt zone (which is what I'm trying to taper) just above that. So the tapered area should extend, say, 1/2" above there. So about 1 1/2" of tapered area. ~3/16" reamed out on the end of the bolt. Okay then, Looks like 1/4" is out, b/c 3/16>5/64. How deeply can a 5/16" bolt be reamed, assuming it's exactly centered and we touch the thread on the outside? Only ~3/4"! Something's wrong somewhere?

I'm trying to make the melt zone shorter, not the molten zone! I need to find a reamer with a lesser slope. I found one called a "taper pin reamer" and the one needed for this job is "2/0" size.

I'll use the taper pin reamer to add a taper to the melt zone, above the heater block.

Bill of Materials, Tooling

GJ trip for extruder parts I'm going to junction today to buy the hot end parts (I'll be getting several bolts and acorn nuts, and enough washers & jam nuts to make two hot ends)

Fastenal 243-5754, pn 75170: brass ¼20 acorn, ea. ¼20 no more than an inch. 5/16 3" 10 in the ¼20 4", $17.90, 5/15 3" $40.25 for 25 of them.

Peachtree hardware on north has the acorn nuts but not the stainless steel bolt. 970-245-1736

Classic computer in delta has heatsink compound, little syringe full for 8.95. I'd prefer something cheaper (in both senses of the word) but that's available today, so I'm going to go for it.

I found a tool that would work for putting a taper on the inside of the extruder. It's 1/4" per foot taper, called a "taper pin reamer" designed for making tapered holes for a tapered pin.

More info on taper pin reamers: has a pdf which lists gauge sizes, with tip and end sizes in decimal inch for each end of each reamer. According to that I want a '5/16" (2/0)' size, which has a tip of .1137 (<.125) and a large end size of 0.1638. It's flute length is only 1-9/16", but the overall length is 1" longer, so I should be able to get it deep enough in the barrel to taper the melt zone! Found a 2/0 for 7.25+shipping which was the best price I found. But their order page didn't load after giving them my CC#. I guess I'll have to wait till Monday to see if they received my order... The taper isn't essential to extruder operation, but would help especially with some types of plastic. (PLA?)