Tool holder screws mushroomed?

I have an emco v10p lathe with the original 4 tool toolpost. Some of the screws in my toolpost have mushroomed where they meet the tool to the point where they are non removable and I cannot put a 1/2 inch tool in at all. The threads are also very tight even when loosening. I’m assuming most of this is from over tightening. Is this normal? Do I take the old screws out, run a tap through the holes and then put new screws in? To add to this I just broke a screw trying to loosen a tool.

I had a tap break inside a tail stock ram for a old lathe. A friend suggested that I take it to a EDM machine. Found a place and they took the ram and said come back in 1-2 hours.
Got it back and carefully tapped the hole. Cost was $50.

A tool post should not be so bad. You could even use a Dremel tool to grind down the exposed mushroomed threads to allow you to back out the screws.

With the mushroomed ends, they are normally turned down so you can screw them out with out fouling on the female thread minor diameter. If they are even more worse hold the screw with a spanner a run a file round to remove the mushroom then screw them out.

Then as you said clean them out and tap them through, if the holder is hardened use an old tap so as to not blunt a decent one.

If your going to replace them with standard cap heads or something thing of the like, take the time to turn the end down so when they mushroom they can be screwed out next time round

But yer it is normal for them to get all right from deformed threads and crap build up.


Or you can do the opposite and mash a angle grinder across it, your choice!

spray some lube like wd-40 to screws, "tighten" to get most of thread to "tool side" and lop off the screws with angle grinder. No need to dick around with them if they are already badly mushroomed.

I've had similar jobs where I've used the side of a cut of grinder disc to grind down past the mushroom so you can back the screws out. Not sure, but on some holders you can use a screw that's short enough to fall out if screwed all the way down.

Screw them down as far as needed then get in there with the skinny wheel on a grinder.

You can run a tap in the female, it shouldn't hurt anything.

I also discovered that it is a mistake to use low grade screws in tool holders when I made the first holders for my quick change tool post. I used stainless steel cap screws because the looked cool. They were significantly softer than the standard, oxide finish cap screws which are grade 8 (quite hard). It did not take long for them to mushroom and I could not back them out.



I used a Dremel tool with a reinforced cutoff disk to cut off the distorted ends ends and replaced them with the grade 8 cap screws. I have not had any problems since. I also rounded the ends of the cap screws so any distortion would start at the center; you can read about doing that in my plans for the QC tool post.

Quick Change Tool Post for Lathe - HomemadeTools.net - Page 3

Cut your distorted screws off and toss them. Replace them with grade 8 cap screws or set screws.

I like stainless too, until it galls out on me.

A side issue is how did those screws deform. If the end is mushrooming then the hex head must not look so great.
I use hardened set screws and have had a couple of rounded-over hex keys and screws. But the other end has never mushroomed, 24 screws total in 6 tool holders.

I use brass tipped screws like these:
McMaster-Carr
Easier on the holders.
Bob