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| Hardening a tap |
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| ieezitin:
I have made a .635 OD x 26TPI tap and now want to harden it but considering the fine thread I have i dont want the edges to spark while heating, what are the suggestions to stop this, i think its a 12ln steel but not sure. Anthony.. |
| awemawson:
As I'm sure you realise, the issue is excluding the oxygen while the process progresses without inhibiting the cooling when plunged into the quench of your choice. I've used stainless steel foil - excellent for the heating but definitely affects the quench. I've used fire clay slurry which works ok but can flake off if you get too impatient heating too fast. Best I've found is 'Zircon Dip' which is sold by foundry suppliers for coating high temperature ladles and the like. A quite thin dip will survive both parts of the process |
| philf:
Anthony, Another possibility is to wrap the tap tightly with iron wire. This technique is used in clockmaking. In addition a coating of borax will help to keep oxygen at bay. Phil. |
| Meldonmech:
Hi Anthony I use iron wire for the wrap then completely cover with ordinary household soap, well rubbed in. I heat the mass slowly in a Bunsen burner flame or gas ring depending on the size. This ensures more even heating. Depending on the tap material the tap can be quenched in new engine oil, or water. Oil is less severe than water. After hardening if the tap is high carbon steel it will need polishing and then tempering to light straw colour. This is best achieved using a small steel lid filled with fine sand, to evenly heat the tap, and carefully heated from beneath until reaching the required colour, then quenched. If you are not experienced in this technique, try it on a similar size nail, as the timing can be tricky. Good Luck David |
| Fergus OMore:
--- Quote from: philf on August 01, 2015, 07:06:54 AM ---Anthony, Another possibility is to wrap the tap tightly with iron wire. This technique is used in clockmaking. In addition a coating of borax will help to keep oxygen at bay. Phil. --- End quote --- Digressing( a wee bit) But where does one get borax now? I've been looking for some to mix with sugar. No- it's for killing cockroaches! Yes, I've been using a white silver solder flux-today, but is it borax? Cheers Norman |
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