The Home Machinist!

one bolt is short - tapped blind because it is under one of the steam passages.

most, if not all of the others go through and get a nut...

if i remember correctly. it has been a couple of years and i don't have all my files here in Sweden with me.

johnpenn74 wrote:This is a little off topic, but does the bolt for the aforementioned tapped hole go all the way through the cylinder casting? Do all the others do the same? or just studs out of the casting?

JP

No, it's a blind hole .188" deep. The other five holes are through holes.

I may try to use alum (potassium aluminum sulfate) to dissolve that broken piece of tap out. Heading to the store during lunch to see if I can find some.

Hi,

If you have a complete set of taps it helps a lot. I have taps from #0-80 on up to 1/2" plus quite a few ME taps. If I'm tapping #5-40, I use a #4-40 tap first to partially cut the threads. This reduces the load on the #5-40 tap when it cuts. You can also do the same thing for #8-32 and #10-32. I also alternate bottoming, taper and plug taps, especially for blind holes. Tapping small holes is always a bit nerve racking, but I break very few taps. One of the hardest holes to tap is #6-32 because the root dia. is the smallest compared to the depth of thread so the tap isn't as strong and it has to remove more metal as it cuts.

I have used a Dremel with a diamond burr to remove a broken #5-40 tap in the past and salvaged the part. It works, but its a long, slow painstaking process and you really need a microscope to do it properly. My friend Don says he uses small carbide end mills to do the same thing. That seems to work for him. Its better not to break taps in the first place.

Taps are amazingly strong as long as you don't bend them; they don't like that at all. Most importantly, you also need a good cutting fluid. Varsol works great for aluminum.

Just a few things I've picked up over the years.

Richard Trounce.

toss the part in a glass of vinegar with a pinch of salt and leave it overnight. Tap will fall out.

or put it in some dilute battery acid if you have it.

do no run the risk of damaging the surface - you do not have a lot of gasket area there to play with

Bill Shields wrote:toss the part in a glass of vinegar with a pinch of salt and leave it overnight. Tap will fall out.

I have never tried removing a tap with the salt-vinegar method, but do know that it does a wonderful job of removing the mill scale from hot rolled steel.

Do not do this process near anything that you don't want to rust, as the fumes will rust anything near the solution.

Regards,

Doug

RET wrote:Hi,

If you have a complete set of taps it helps a lot. I have taps from #0-80 on up to 1/2" plus quite a few ME taps. If I'm tapping #5-40, I use a #4-40 tap first to partially cut the threads. This reduces the load on the #5-40 tap when it cuts. You can also do the same thing for #8-32 and #10-32. I also alternate bottoming, taper and plug taps, especially for blind holes. Tapping small holes is always a bit nerve racking, but I break very few taps. One of the hardest holes to tap is #6-32 because the root dia. is the smallest compared to the depth of thread so the tap isn't as strong and it has to remove more metal as it cuts.


Richard Trounce.

I like those ideas. I never thought about doing that and always wondered why 6-32 taps were so hard to use.
thanks,

Picked up alum at Wal Mart this evening and she's a bubblin' away now. The bubbles on the casting are from when I dunked it in the solution. The steel is giving off nice large bubbles, albeit slowly, so it's working. No idea how long this will take. I've got it in a Pyrex 9x9 dish wrapped in aluminum foil and sitting on the stove on low heat. No, I'm not going to leave it on all night!


Meanwhile... onto other parts. After the tap fiasco I decided to go with the easiest casting in the kit, the spacer:


After facing both ends and boring the center, time to drill the hole pattern for the studs:


I'm beat for today, so that's it for now.

After a couple days in the alum solution, the broken tap doesn't appear to be affected much. I have no idea how long it will take on HSS... so, here's my plan. I'll hold off on doing this until later to see if you all think it's OK.

I'm going to chuck the valve head back into the 4-jaw and center it on the hole with the broken tap. I'll machine a thin groove as close to the edge of the hole as possible, then remove the tap piece with it still stuck in a small amount of the bronze. Clean up the larger hole I just created and turn a brass plug to silver solder into the enlarged hole. Set it back up in the mill, drill, and tap the hole again, this time in the plug.

Thoughts? Ideas?

I'll machine a thin groove as close to the edge of the hole as possible, then remove the tap piece with it still stuck in a small amount of the bronze. Clean up the larger hole I just created and turn a brass plug to silver solder into the enlarged hole. Set it back up in the mill, drill, and tap the hole again, this time in the plug.

I have done the same thing in steel. Worked for me.

John B.

i would let it soak.

this is a casting that is full of passages. get the plug in without silver solder everywhere around and under it, and you can end up with a leak.

try some battery acid.....it WILL come out, just do not be in a hurry.

How about a tap extractor? It's a tool with little fingers that slide down the flutes, knock the chips out of the way and let you grab the stub to remove it. I've used them and they have worked for me. You have to buy one for the size and number of flutes of your tap. Here's the McMaster page that lists them: http://www.mcmaster.com/#tap-extractors/=l7wa2u

Didn't get much shop time today, but I did get the spacer casting finished up as well as the bottom cap.




Still debating my fix for the broken tap.