Making spaced threads to fix in timber.

[campilialex]

Hi guys, I am wanting to make some treehouse attachment bolts but I am unsure on the best way to tackle this thread.
I am using a manual lathe, the bolt will be 40mm diameter and be made from 4140 steel with a 5mm pitch thread.
1.how would you achieve the below thread style with the wider root?
I was thinking I could grind a hss steel to match, like in the photo, but not sure if this should be the exact width of the root, so come in like a plunge cut, or have it narrower, so come in to depth and then move the cross slide across to widen it up. Will HSS leave a good finish with 4140? Happy to answer any other questions. thank you!

 

[Shootymacshootface]

If it were me I would thread it in reverse with the tool upside down, thread from the fastener head to the tailstock, and stagger your starting points.

 

[mmcmdl]

If it were me I would thread it in reverse with the tool upside down, thread from the fastener head to the tailstock, and stagger your starting points.

Or , just give it to one of my machinist's at work . They come up with some threads I've never seen before . ( in a nice way to put it )

 

[francist]

the bolt will be 40mm diameter

40mm diameter?

 

[benmychree]

I made a bunch of lag bolts like that years ago, I made the tool the full width of the root and went in at the angle of the tool, like cutting an acme thread, and note that I used a good deal narrower angle than you show, look at the thread angle on a commercial lag bolt. I did not do the gimlet point as with commercial bolts, as they were threaded into drilled holes.

 

[matthewsx]

I would not make it with a Philips head unless you have a really big screwdriver.

I hate to ask since this is a forum of makers, but why would you make such a fastener rather than buying them?

John

 

[benmychree]

I would not make it with a Philips head unless you have a really big screwdriver.

I hate to ask since this is a forum of makers, but why would you make such a fastener rather than buying them?

John

The ones that I made were 3/4" diameter and several feet long, and were used in big timbers used to secure big bearing blocks in repowering a historic water power grist mill that I did a lot of work on many years ago, it is part of a state park, originally built in the mid 1840s, the state rebuilt it, and had a eastern millwright recreate the gearing to power it a state employee and I installed most all of it, I think I remember that the shafting was 3 -15/16" diameter, the millwheel is about 46 ft in diameter, drives 2 stones, one for wheat, the other for corn, they are 5 ft diameter.
Google "Old Bale Mill" it will likely come up.

 

[campilialex]

Thank you for those responses.

note that I used a good deal narrower angle than you show

Would you know what angle thread would be suitable for this? my drawing above was just a standard 60 deg but as i do intend to thread them into a pre drilled hole, they should probably be more narrow. so did you make your own hss bit for this?

I would not make it with a Philips head unless you have a really big screwdriver.

I hate to ask since this is a forum of makers, but why would you make such a fastener rather than buying them?

That was just something i found quickly on the net to show the thread style, definitely wont be using a Philips head. I've attached some photos of some of the tree house bolts they use in the US and Germany which i want to replicate. I cannot buy these in Australia otherwise I probably would. Sorry should have attached these initially -

 

[benmychree]

I ground my own tool, suggest that you find a commercial lag screw and imitate the angle used.

 

[matthewsx]

Okay, that's something I can see making on your lathe. How many do you need?

John