Thread: tapping problem

Hi Joe,
You can still get them and online from here
https://www.bolt.com.au/bright-squar...1021_1023.html
The metric 8 are around $2 each so not cheap, but if you only need a few it's not to bad I suppose.
They also have BSW
https://www.bolt.com.au/bright-squar...1021_1022.html

They are all cup points.

Dave

Originally Posted by jhovel

I find that my socket screw heads constantly fill up with swarf and then the allen key doesn't go all the way in and rounds off the top part of the hole.

Ahh, I hadn't considered that. Anyone else have this problem? Always wondered why they use square heads. Now it makes sense.

With mine I clean the swarf out first,by using a small magnetic point of some description.
Other times if working with none magnetic material I will use milk bottles cut up to cover the top of the post.

Why not ring Hercus (08) 8346 5522 and find out what they would do. They would know the degree of hardening. A new toolpost may not be very expensive!
It is a common problem on cheap Chinese lathes for the tool holding bolts to be too soft and the ends "mushroom" by too much clamping force onto the tool.
Your lathe may have had the original bolt replaced with one of these "soft" ones.
Your attempt to wind the damaged screw out, may have damaged the lower (bottom) thread and it may be able to be ground off with a small wheel in a Dremel or similar grinder.

Hercus no longer manufacture or support the lathes. The product is at least 20 years old and most likely more than that. Having said that, they still have some parts left and there are still a couple of guys there who are very generous with their time when owners get truly stuck. Hopefully guys aren't wearing out this generosity by constantly badgering them with trivial enquiries. There are some smart minds here, and I'm sure a solution can be found.

Before anyone shoots me down, as I'm sure they will, consider what sort of support you would get if you rang up Holden head office and wanted to know how to fix a faulty door handle on your EH Holden

Pete

Originally Posted by jack620

Ahh, I hadn't considered that. Anyone else have this problem? Always wondered why they use square heads. Now it makes sense.

My tool holders use square head bolts and hex deep hex ones to tighten the QC and to rotate it. I have socket head bolts holding the cross slide onto the apron below the tool post, and even though I don't need to undo them, they collect the swarf all the time.
A standard hex head bolt could be filed into a square head but is wont be as deep, though you could weld on top of the head before filing to make it deeper.
If I was going to do them I would weld onto them, then machine them round (to the size of the bolt head diagonally) in the lathe as well as face them off before filing square.

Dave

Originally Posted by Dave J

They also have BSW
https://www.bolt.com.au/bright-squar...1021_1022.html

Good find Dave. From what I've been able to find out, 5/16 BSW screws are interchangeable with 5/16 UNC, so they should fit my tool post.

I might order a set and avoid the swarf issue.

Chris

I thought BSW was 55deg and UNC 60deg?

You might be right. This is where I got my info (see Question 27):

https://www.stainlessstore.com.au/faq.php

British Standard Whitworth - Wikipedia, the free encyclopedia

http://www.britishfasteners.com/threads/bsw.html

UNC Thread Profile

By "interchangeable" I think they mean the nut of one standard will fit onto the bolt/screw of the other. That might be OK for non-critical situations, but not for a piece of machinery.

I imagine a case-hardened BSW screw (55 degrees) would damage the UNC thread (60 degrees) in my non-hardened TP.

I sent them an email pointing this out.

Thanks for clarifying Fred.

Originally Posted by jack620

Good find Dave. From what I've been able to find out, 5/16 BSW screws are interchangeable with 5/16 UNC, so they should fit my tool post.

I might order a set and avoid the swarf issue.

Chris

Chris
5/16 BSW is 55 degree with 18 threads per inch
5/16 UNC is 60 degree with 18 threads per inch
Close enough to being the same. If final fitting is needed then easy enough to run a threading tap to tidy up the slight variation in thread angle.
regards
Bruce

After all these years of use the threads would have a bit of wear, so they will probably go strait in.

Dave

Whitworth bolts will fit right in as thread angle difference will not be enough considering the wear. One problem I see is that whitworth is usually mild steel. I just went to town and bought my 1/2" UNC bolts from local general supply shop. If you find an engineering supply shop I would be supprised if the correct UNC bolts could not be bought over the counter. Use high tensile bolts to minimise bolt expansion from constant tightening!

The main reason for using a particular bolt is the ability to tighten them using a T handle so if you don't want to use allen head then buy a socket and extension to weld a T handle too. The purpose is to tighten the bolts easily. A hex head bolt will be fine if it sticks up enough for the T handle to slip over enough for it to stay in place while it is rotated quickly. Hex, allen or square doesn't matter, you want an arrangement that will allow you to spin the bolt in and out fast with a T handle like the chuck!

I have never had a problem with swarf inside my allen heads but then my tool post is bigger than most and higher. I would use air to clean them out if I had to, but I don't recall having to, up to now. I don't see any need for a QCTP as I think my setup is nearly as fast and a lot cheaper. I engrave the tool height on each tool holder so I can calculate the spacer required to set centre height. I could engrave the spacing needed but that would change If I got a new lathe, which is a dream for me! But hey, a couple of years ago owning a lathe at all was a dream.

Dean