Cumaru or IPE and Thread Inserts

[Brad Shipton]

I can't find the knockdown inserts below in my town to do a test, so I am hoping someone can shed some light on this for me before I order enough for the complete project. I am working on the Cumaru box newels and railings for a custom deck project that is not to have exposed fasteners, and needs to come apart in the future if they damage any of the aluminum pickets. I am toying with the idea of using the inserts below, but given the past problems with brass inserts in hardwoods like this, I am not sure this is going to be a great solution. I like the idea of these since they can be installed easily with a hex key. I have a few other ideas that might work too, but they are not as easy as this will be.

http://www.leevalley.com/en/hardware/page.aspx?p=44237&cat=3,43715,45375

Thanks everyone.
Brad

[Peter Pedisich]

these things strip out very easily when installed with a hex driver bit. You can use a threaded insert tool which 'threads' into it which is better, and making a proper sized hole for hardwood and dipping in a toilet bowl wax ring prior to installation.
I would not rely on a cast zinc insert for a newel post in end grain, for sure. Can you use barrel or dowel nuts with bots from below and plug them with face grain plugs?

[Brad Shipton]

Thanks Peter. The barrel option was one of the other ideas, but it is a little more work to put them in. I have something like 60 of them to do. The bolts are only needed to tighten the joints. There is a tenon the rail sits on. I would simply screw the rail to the tenon if it were not for them wanting the rail to be removable and no exposed fasteners. Originally I was going to use the ol domino to put the whole thing together, but that kinda got scraped along the way.

Brad

[Jamie Buxton]

With strong hardwood like ipe or cumaru, you can just drill and tap the hardwood directly. Get a couple screw-diameters worth of thread, and the screw is never pulling out. Try it. You can lever on it with a claw hammer or a wrecking bar, and it won't come out.

[Brad Shipton]

Thanks jamie. I thought about trying that, but was leary since it is wood. I have tapped a lot of aluiminum lately, so i will give it a whirl. Do you hand tap or do in a press? It is pretty easy to mess up threads by hand. I was trying some brass inserts today and two out four didnt work very well.

Brad

[Jamie Buxton]

Thanks jamie. I thought about trying that, but was leary since it is wood. I have tapped a lot of aluiminum lately, so i will give it a whirl. Do you hand tap or do in a press? It is pretty easy to mess up threads by hand. I was trying some brass inserts today and two out four didnt work very well.

Brad

I install threaded inserts with a driver made of a long bolt with two nuts jammed together on the end. The length gives me good aim to run the insert directly down the pilot hole, not in at some weird angle.

Standard metal taps are more inclined to go straight into the pilot hole. They have that long lead-in area at the front.

In my view, inserts are better than direct tapping if the person inserting a machine screw into the hole is not me. The metal inserts are more resistant to cross threading. Me, I know to turn the screw backwards until I feel it drop into the threads, and then I go forward. That technique ensures that I won't cross-thread the directly-tapped threads.

[Steve knight]

the brass are ok for softwoods but thats it. I have installed thousands in tropical woods when making my plans. the holes need to be a bit oversized too. I can't remember the reamer size I used but it is at least .01 larger. the normal hole size is .375 but my reamer is .387 or .39 I think.

[Larry Edgerton]

You can get what you need to try it in most lumber yards. The inserts for holding Newel posts are what I would use, but I would not buy them at the lumber yard if you need very many. Check with a company like Fasteners that specializes in that and buy a full box. They are about $5 apiece at the yard, and about 50 cent if you buy in bulk.

Sounds like a cool job.

Larry

[Brad Shipton]

I experimented with threading the cumaru, and was quite impressed with how well it worked. A few of the threads near the top were not perfect, but once I got past about 1/4" deep they turned out very well. I experimented with the amount of force needed to strip the threads, and it took a reasonable amount of force with a large wrench.

I found EZ-lok makes stainless steel and steel inserts that look a lot better than the typical import stuff. In the end I think I will go to cross dowels to make sure I don't have any problems. I am pre-finishing the parts and I dont need any headaches on site. Its only one extra hole to drill, so its not a big deal.

I really appreciate all the help.

Brad