Can you install Helicoils before Chromate Conversion?

[Chipmakr]

I have some parts made out of 6061-T6 aluminium that I would like to fixture in the last OP using some holes that are tapped for a 6-32 Helicoil. I was curious if I could install these heliciols before Chromate Conversion. I think there will be a reaction in the bath but I am unsure.I had this idea late in the day and no one was there when I called over to the coating house to ask them. So I thought some of you guys might have had some experience with this. I tried getting some 10-32 nylon bolts to use in the holes without helicoils installed but I think I would probably just end up breaking a peice of nylon off in the hole after trying it in a few holes. I wish someone made STI bolts for this situation.

[gcode]

I'm thinking this is a really bad idea..

[J Coulston]

I have machined helicoil bolts in the past, worked great.

[Guest SAIPEM]

If you really want to tick off your finishing vendor, go ahead and put them in.

 

Otherwise, it will be a really good idea to put the inserts in after chromate.

[Colin Gilchrist]

They make a Helicoil removal tool. You could potentially install them for the machining operation, then remove them before plating. Once back from plating, you could then install the inserts permanently.

 

I would not try to send those parts to the platers with the inserts installed.

 

I'm with John, in the past when I needed to use the STI tapped hole for mounting, I just whipped out some custom bolts with the correct diameter/pitch. It is fairly easy to take a grade 8 SHCS that is a size or two bigger and turn them down to make custom shoulder bolts. Just make sure the Minor diameter of the SHCS you are turning is bigger than the Major diameter of the new bolt you need. (If you do this, be very careful how much torque you apply when clamping down the part, as your custom bolts now have very large heads and hex keys, compared to the size of the threads)

[Newbeeee™]

As long as the wire inserts are stainless, it's ok to fit 1st then chromate.

Stainless does not react in a alocrom bath.

We do it on a couple of jobs with small threads, because once alocromed it becomes a nightmare to get the inserts wound in.

BUT get your customers permission 1st, and just tell the treatments company what you're planning on doing

[Guest CNC Apps Guy 1]

IIRC at a company I worked for, we plugged and/or masked the helicoil holes before processing because they were a real bear to get in after.

[Guest]

I have had to put the holes in after plating because they didn't want the additional masking cost.

 

Not being an expert on plating by any means but I think your thought of different metals messing with the bath is spot on.

[Chipmakr]

I was surprised last light by a late night return phone call from the coater. They said it should be ok with SS inserts and that the only potential problem could be liquid and/or contamination getting trapped behind the coils. I am still kind of nrevous to do this to some pretty expensive parts that I am already running late on. I think I will modify some bolts to fit these STI holes. Thanks for the input guys.

[crazy^millman]

Do what I have done for years and make STI bolts. I for #10-32 I would use a 1/4-20 bolt that was long. Put it in the CNC lathe and then turn the STI threads on the end of the bolt. I then can use the STI threads to hold the part without having to put the Helicoil inserts in the parts. It works great and gives to tons of flexibility to make parts without worry of adding tabs and others thing to hold a thin walled part with helicoils.

 

HTH

[Newbeeee™]

Chromate conversion (Yellow as in alocrom/alodine 1200) is what it says - a conversion and not a plating.

Plating builds/adds thickness, conversion coatings don't but chemically change the material structure to a high chrome content (chromium trioxide).

This is why you can successfully alocrom sheet metal and then bend it without any degredation to the coating. The high chrome content also makes it very good for electrical conductivity (bonding/earthing) and corrosion resistance.

The problem you get is chromate increases the friction when fitting inserts.

So if you have very small inserts, the wire gauge is obviously very small and weak. Winding these into alocromed threads usually breaks the drive tang off when you're about a turn from fitting.

Also, if you have 1.5D inserts (or longer), this is also a problem as the friction builds up and up when fitting the bloody things, to the point that the drive tang bends/breaks even on larger thread sizes.

The best way I found was fitting these with paraffin, or talking the drafty boys out of specifying them altogether!

And to repeat - stainless steel inserts (beit wire thread or pem standoffs or studs) are not affected by the process at all. They don't cause harm to the mix/tank and the conversion doesn't affect the fasteners at all (providing they are stainless).

[BenK]

I have machined helicoil bolts in the past, worked great.

 

 

 

+1

This is how we do it.

[taperlength]

If a lathe is not available you can make STI bolts on a mill by external thread milling.