My first injection mold and the Rabit HY-4 injection molder

**gavztheouch** · 13-10-2014

Sounds tempting Robin but I don't think my myford will be able to work something that big.

**gavztheouch** · 18-10-2014

Anyone got any ideas as to what a custom made carbide or hss tool would cost to cut the profile for my injection mold "nozzle gate" as per drawing?

**mekanik** · 19-10-2014

Can you make one of these

D bit.doc

**Robin Hewitt** · 19-10-2014

I am still not understanding, isn't this shape ground into steel perfection for you as part of the sprue bushing?

**gavztheouch** · 19-10-2014

Originally Posted by Robin Hewitt

I am still not understanding, isn't this shape ground into steel perfection for you as part of the sprue bushing?

As far as I know you cannot buy sprue bushings for this machine, you have to machine them yourself into the fixed halve of the mold.

**gavztheouch** · 23-10-2014

Originally Posted by mekanik

Can you make one of these

D bit.doc

Would this be possible to make on a standard myford ml7-r?

Im guessing it would need to be quite high quailty steel? Hss?

**mekanik** · 23-10-2014

Hi Gav
Yes it's made from silver steel which is a high carbon steel available in metric & imperial sizes and is ground finish and readily available. The bar is in it's annealed state and you manufacture your required tool then heat it to cherry red and quench, then polish the tool and apply heat to the end of the shaft and you will see the polished surface change to a straw color as this works it's way to the cutting part of the tool quench in cold water and that's it tempered.

Looking @ your drawing that profile is situated in the sliding part of the jobby that the mould goes into,is that correct ?

**Neale** · 23-10-2014

Making those kinds of countersink bits in silver steel on a Myford is fine - done it plenty of times myself. The biggest issue is machining the half-diameter; you can file it, but I used my Myford milling slide to machine it. Even easier if you have access to a milling machine. If you make a slight undercut just where the cutting surfaces meet the full diameter, you end up with a flat surface that is easy to touch up on a stone if needed. Hardening is one of those odd things that sounds very difficult and technical but is actually very straightforward when you do it. Main thing, as Mekanik said, is to heat the shank. not the tip, and watch the colours travel towards the cutting edges, but don't use too much heat as the travel can be a bit too quick. If that does happen, you can always try rehardening (cherry red and quench) and then have another go at tempering. Silver steel properly hardened and tempered actually cuts mild steel surprisingly easily; what it can't take is heavy/fast cutting which overheats the cutting edges and destroys the tempering. That's one reason HSS was invented - holds its temper even when pushed hard.