Thread: tapping problem

In general the Hercus post is not hardened.

The Square head set screws normally are.

Have you taken an other screw out and screwed it into the hole you have been running your tap through.

The plug tap should be fine for what you are doing.

If you have put a tapping drill through the hole that would indicate that the hole is as round an concentric as the drill.

The bottom of the screw that you removed appears to have the bottom threads missing.

Was the screw allways like this or did this occur as or after removing it from the tool post.

If it ended like this after removing from the post there is a good chance that the missing threads are locked into the bottom threads of the tool post.

Might pay to try and see with the limited amount of room available if something is caught in the bottom threads.

If you think that there maybe something there I would try running the damaged set screw back into the hole to see if you can dislodge the offending item,you want have anything to loose by trying.

Originally Posted by pipeclay

If it ended like this after removing from the post there is a good chance that the missing threads are locked into the bottom threads of the tool post.

......

If you think that there maybe something there I would try running the damaged set screw back into the hole to see if you can dislodge the offending item,you want have anything to loose by trying.

I hadn't considered that possibility. I'll give it a try. If that doesn't work I think I'll take up the other suggestion of using the Dremel to remove the offending metal. I've got a diamond tipped bit for the Dremel.

I just cleaned up a few "scars" on the tool-post (not mine) with a file and the metal was quite soft.

I reckon I will also replace all of the screws with socket head screws with the ends turned down as also suggested.

Thanks to everyone for your help.

I have had good luck with the thin cutting disc's on the dremel. Just wear it down on some scrap steep until it fits in the hole and follow the threads.

Dave

pipeclay's suggestion of running a screw thru the hole worked. I was then able to clean up the threads with the tap.

Never fails to amaze me how an apparently simple job can turn into major saga.

I bought a set of socket head screws to replace the old mushroomed ones. I'll turn the ends down to remove some of the thread as Dave suggested. Any tricks for doing this? I don't have carbide tools, so hopefully the HSS will cope with the hardened steel screws.

It must have been someone else suggesting to turn the ends down. (just had a look and it was Dean)
For the new bolts, you could put 2 nuts on it, put it into the 3 jaw with the threads facing out and so the front nut is just protruding, then put another nut on it and tighten it up to lock the bolt. You will be fine with HSS cutting it.

Dave

Sorry, you're right, I meant Dean.

Thanks for the info.

No problems,
While they are in their, face the ends as they rarely come true.
If you want to stop them rusting up after machining, give the tip a heat up with propane until the are red and dip them in oil. I find dirty motor oil brings it out nice and black.
You can also just use the BBQ, and hold the bolt over one of the burners with the plate off using long nose pliers or similar.

Dave

Dave,
I've got an oxy torch and a MAPP gas torch, so no need to fire up the BBQ! Doesn't that damage the temper of the screws?
Chris

If you just get them red with the Mapp you should be right.

Dave

do a quick spark test on the tool post to see how hard it is. does a new bolt scew in to the tool post very far? if so screw one in and give it a sharp tap with a hammer. then try tapping again. tapper tap sounds like a good idea.if you can borrow one even better
aaron

Thanks Aaron, but I sorted out the damaged thread problem. Now sorting out how to make new screws from socket head screws.

opps all ready solved the problem well done.

Hi Chris ,
There was a post a few days back about holding bolts in a nut that is cut through on one side so tightening the chuck jaws grips the bolt. I cant remember where it was though.
Stuart

As it has been correctly determined it was me who suggested removing the bottom threads (not an original idea by the way just copied) I will explain that I gripped the cap screws using 2 nuts as suggested by Dave. The split nut idea sounds like a good one too. Wish I had thought of it as I would have preferred more than one nut in the chuck, or maybe I did. 3 nuts altogether with one single nut further in to support the head end. With split nuts 2 could be used and placed anywhere. Machine to less than minor thread diameter to allow for metal expansion from constant tightening.

Certainly face the ends of the bolts. These bolts will have a hollow end with sharp edges from the thread rolling. They will damage your tools. I use a strip of mild steel packing 1mm thick under the bolts to protect my tools as well.

Remove bolts regularly to ensure the end has not expanded to greater than the thread minor diameter. This is cheaper than cutting them off and buying new ones. I had 2 different diameter bolts in my post so some had already been drilled and retapped. I don't think it will need to be done again before the lathe is cactus so I have driiled and tapped all to match. 1/2" UNC will last forever anyway.

Dean