Screws: Cut vs. Rolled Thread?

McFeeley's offers two types of brass screws: cut thread and rolled thread.
Fasteners->Screws->Flat Head->Brass http://www.mcfeelys.com/subcat.asp?sid%0
I inquired at McFeeley's site using their online form asking for them to contrast the two types and have not heard back -- I suspect their email inquiry mechanism is overwrought with spam, or my spam filters annihilated any response. Consequently, I seek the wisdom of this more advanced woodworking group on the question:
What are the advantages and disadvantages of cut thread screws and rolled thread screws?
Comparing #8 x 1" Flat Head Brass Square Drive reveals: Cut Thread: $12.88/100 Rolled Thread: $8.92/100
Cut Thread has about a quarter of its length as a shank (no threads), Rolled Thread has less unthreaded shank. In comparing the two diagrams, the rolled threads seem more pronounced and may have more of a "bite".
Thank you, in advance.
John
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

They provide the information, free of charge. http://www.mcfeelys.com/tech/cutvrolled.asp
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
John L. Poole wrote:

For the manufacturer, the advantage is a rolled thread screw can be made in two steps with no loss of material. Roll the thread onto a wire blank between a pair of hardened comb plates, then forge the head between dies.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
The threadrolling operations I've seen use a heading machine to form the head (bolt, screw, nail) then off to the threadroller to roll threads ( or rings on nail ). One advantage for the manufacturer is a larger diameter product with less material. It work hardens the metal in some cases.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

The thread rolling operation yields a screw or bolt with superior fatigue properties. It is hard to see how rolled threads would be needed on a wood screw.
Jim
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

They grip better. Easier to make a pilot hole with not taper. Seems like most are made that way if you read the info McFeelys gives. From what I can see, it is roll from a wire, unlike some threaded bolts that jus roll the shaft to form the thread.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Edwin Pawlowski wrote:

I've never seen a rolled-thread bolt. If it's rolled, then it's a screw. Bolts _must_ have a plain shank, and must have a plain shank that's larger in diameter than the screwthread. They're basically dowel pins for use in shear with a threaded locking mechanism, not axial clamps (i.e. screws).
(please check your Machinery's Handbook before posting a rebuttal)
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

IMO, brass screws need all the help they can get.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
George Max wrote:
> IMO, brass screws need all the help they can get.
I'm with you, given a choice it's bronze or S/S for me.
Lew
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Jim wrote:

Bike spokes have been made with rolled threads for years for this very reason.

They're not.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Father Haskell wrote:

They are however much cheaper to make and much easier to work with..
Upset heading and thread rolling can make 3000+ parts per hour with almost no waste, a screw machine is closer to 350 and produces a lot of scrap.
The tapered pilot holes and increased cost keep the market for cut threads limited.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Sat, 13 Jan 2007 18:39:03 -0800, "John L. Poole"

FWIW: From the Lee Valley Web site:
"These are all cut brass screws with well-defined threads and strong necks, unlike rolled brass screws, which tend to have rougher threads and are invariably weaker. "
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
<snip>

Fascinating. You would think McFeeley's might address the conclusion that rolled screws are invariably weaker, if only to state it to help the buyer decide. Referencing the page Edwin so kindly provided a link to: http://www.mcfeelys.com/tech/cutvrolled.asp
Given the weakness of brass to begin with, I'd certainly want to know if two kinds of brass screws vary in strength. Of course, we're not comparing apples and oranges here since McFeeley's offers cut threads that are slotted and square drive that are rolled. Maybe a square drive rolled thread is less likely to fail than a slotted cut thread??
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
The US Forest Products Lab seems not to have weighed in on this yet with published experimental data either. http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr113/ch07.pdf contains data and analysis from the pre-rolled thread era. An FPL tech pubs search on 'rolled threads' yielded only one reference and that pertaining to ring-shank nails.
These folks put forth some recommendations (see page 8) http://www.pdhonline.org/courses/s168/s168content.pdf however I haven't seen the research on which it was based so can't comment on its veracity.
Some theoretical observations for the technically inclined:
One must distinguish between the strength (or weakness) of the fastener and that of the fastened joint. In wood joints, failure most often occurs in the wood, not in the fastener itself.
For joints loaded in shear rather than tension (fastener withdrawal) then, for a given nominal screw size, the rolled-thread screw has a smaller shank (unthreaded portion of screw) diameter compared to a cut-thread screw. Thus, if the shear joint interface falls at the shank then the lateral bearing surface will be lower and the bearing stress tending to compress the wood fibers will be greater.
Conversely, the root diameter of a cut-thread screw is smaller than its shank. If the shear joint interface falls at the threaded portion of the screw then the lateral bearing surface will be lower and the bearing stress on the wood fibers will be greater than if the fastener length had been selected to cause the joint to fall at the unthreaded shank.
For joints oriented such that the screws are loaded in tension, I believe that, unless the threaded engagement is extraordinarily long, the failure mode will be stripping of the threads in the wood (or pull-thru of the head). That being the case the relative sizes of shank and thread root diameter will not matter except as the latter determines the height of the thread.
These are much simplified considerations. Also involved would be wood species, moisture content, grain orientation of both pieces of wood making up the joint. Beyond that overall joint geometry, point of application and orientation of the load, geometry of the fastener pattern, significant deformations of the fastener or joined pieces as failure approaches, corrosion effects over time, etc. One thing that was mentioned that I can see no likelihood of being involved in the failure of a screwed wood joint is 'fatigue'. That is a term applied by metallurgists and structural analysts to a progressive cracking mode of metal failure due to cyclically applied loads combined with microstructure and/or electrochemical irregularities.
Persons screwing together wood joints that are not structurally critical (i.e., failure could cause harm) can happily ignore such complexities and go on enjoying their hobby, following only common sense and rules-of-thumb such as selecting appropriate types of screw and avoiding the use of screws into end grain whenever possible. However home builders, boat builders and similar craftsmen of srength-critial structures need to follow established codes, standards and specifications and seek competent engineering guidance when needed.
David Merrill

to:
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Site Timeline

Related Threads

    HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.