Thread restorer (internal)

[Paul in the woods]

I need to clean up an internal thread on a part for my mini-digger. The part worked it's way undone and damaged the last few turns of the thread. There's plenty of good thread to work with. A quick measurement suggests it's a M30 x 1.5.

 

I would normally buy a tap to do this but a M30 x 1.5 tap seems a bit expensive and I may not have the measurement spot on. 

 

I bit of a google shows 'thread restorers' such as this: https://www.zoro.co.uk/shop/cutting-tools/thread-restoring-files/thread-restoring-files/f/61

 

Sort of a file you align with the good part of the thread and clean out the damaged part. Anyone used them and are they any good?

 

Does anyone have any suggestion of anything else could try?

[Ratman]

I need to clean up an internal thread on a part for my mini-digger. The part worked it's way undone and damaged the last few turns of the thread. There's plenty of good thread to work with. A quick measurement suggests it's a M30 x 1.5.
 
I would normally buy a tap to do this but a M30 x 1.5 tap seems a bit expensive and I may not have the measurement spot on. 
 
I bit of a google shows 'thread restorers' such as this: https://www.zoro.co.uk/shop/cutting-tools/thread-restoring-files/thread-restoring-files/f/61
 
Sort of a file you align with the good part of the thread and clean out the damaged part. Anyone used them and are they any good?
 
Does anyone have any suggestion of anything else could try?

Can you post a pic of the thread?
Thread files are “ok” but are really only designed to dress the thread and not recut, depends what kind / how much damage your looking at and may not do enough for you.

[Macpherson]

Hi, cheap thread gauges like these make it easy to ID the pitch and callipers on the bolt will give you the OD, with a large internal thread like this you might well be able to clean it sufficiently with a dremel type tool and a lot of care, I've used thread files but really only good on external threads.... really all depends how mangled they are and how easy to get at,  Cheers.

 

https://www.ebay.co.uk/i/183359163967?chn=ps&norover=1&mkevt=1&mkrid=710-134428-41853-0&mkcid=2&itemid=183359163967&targetid=1000147646860&device=c&mktype=pla&googleloc=1007336&poi=&campaignid=10199631037&mkgroupid=101938325957&rlsatarget=aud-629407026465:pla-1000147646860&abcId=1145985&merchantid=101717760&gclid=CjwKCAiA8Jf-BRB-EiwAWDtEGqKiGOfneGEJYkcchmSaq8sIWR3waISaZNkm_3eF77sMUVoT9MSR7xoC6AgQAvD_BwE

[dig-dug-dan]

Can you not use an impact wrench to force the bolt in. That sometimes cuts a new thread 

[gobbypunk]

Yep get a sacrificial bolt and wind it in slowly it might cut a new thread ,or how friendly are you with your local tractor repairers maybe you could leave a deposit and borrow a tap the right size I have done things like it in the past ,good luck with it .

[Dan Maynard]

I've cut slots into a bolt with angle grinder disk before, works really well for cleaning up rusty internal threads. I guess depends how bad it's mangled up, maybe worth a go?

[Paul in the woods]

Thank you for the suggestions. I do have a micrometer and thread gauge, and it looks like M30 x 1.5 but it may not be an exact match.

 

The part looks to be cast iron and it screws on the end of a piston on a cylinder. So, I don't have a bolt to force in and I don't want to damage the cast part.

 

I've cleaned out the threads with a metal pick and that has removed some of the loose parts. There is about two turns where the thread has become flattened and could do with reshaping.

 

As the iron looks fairly soft a bolt should do it, or worth trying first. If I can't find one laying about I'll order one. Even a single M30 x 1.5 bolt is expensive and not the easiest thing to find.

 

Noted about cutting slots in the bolt.

[Macpherson]

23 minutes ago, Paul in the woods said:

Even a single M30 x 1.5 bolt is expensive and not the easiest thing to find.

 

Hi, I Thought I remembered that thread size, it's metric fine and a standard size.

 

Your right about cast iron being soft, I spent many years working with it, perhaps you could find another metric tap with 1.5mm pitch and use it as a scraper to reform the thread.

 

Found this hydro hose banjo bolt  which is the right size and not too dear and might be useful to put a slot in or check any repair.. maybe a plant company or hose guy would have these lying around, good luck.

HYDRAULIC HOSE CONNECTORS - M30 X 1.5MM MALE BANJO BOLT HEX HEAD ST 1-10171

WWW.EBAY.CO.UK

---

Green Flow. The Green Spark Plug. RRP £ 0.00.

 

[aspenarb]

The best tools for repairing internal threads are the ones that start at the bottom of thread, you then expand them and turn them out. Trouble with starting at the top with a conventional tap is the danger of overcutting.

 

Bob

 

 

 

 

[eggsarascal]

I'd be having a ring round a few engineering shops, be cheaper than buying a tap of that size.