Carbon fiber tool holder

[Bentwings]

We were sitting back in the rc model aircraft part of the shop and carbon fiber constructions came up. I’m a big fan of composites in rc plane construction eve4 since I was introduced to it years ago.


so while boring a small hole in some 4130 steel I ran into chatter with my small tool. I just could not get rid of it.
it appears the tool is just not rigid enough for the cut and once chatter marks appear it’s hard to get rid of them.

one thing led to another and I began thinking that maybe carbon fiber insert holder would be considerably stiffer. The issue then becomes how to machine or make this new holder. CF does not like to be machined. It will dull the best of tools quickly. It will delaminates unexpectedly wrecking your part. So I thought what if I made the tool as a molded or reinforced part. A fabricated part could get tedious in a hurry. Many standard epoxies don’t work well and the few that do are quite expensive. . So I did look on the internet for such a thing but even though there seemed to be a few there was no information at all on them. .

im noe considering encasing a steel holder in CF FABRIC WITJ CF tow ) very fine thread like fibers) wound directionally to resist bending and deflection. I no longer have sccess to exotic lab testing equipment so results will be highly subjective. I’ll order some epoxy shortly as I have CF materials . I’ll have to get a new insert holder to work with. I though of s very hard wood form reinforced with CF but I don’t think it would work wel . But anyway I think I’ll explore this more. Both searching and asking questions. I certainly can’t be the first to yhink of this.
CF is as much as 10 time the tensile strength of steel and two to three times as stiff.
id be interested in comments.

byron

 

[Bentwings]

Wouldn’t you know my double vision messed the thread name I meant tool holder. Please excuse my dumb error.
thanks

EDIT: Byron, I corrected the title.
Gail in NM

 

[mu38&Bg#]

Carbon fiber composite is not stiffer than steel. Best case, carbon's stiffness is something like 90% of steel.
Use a solid carbide or indexable carbide bar. Carbide is actually ~2-3 times stiffer than steel. In larger sizes dampened bars are common.

 

[Peter Twissell]

When we talk about relative strength and stiffness of materials, it is important to say whether it is by weight or size.
I understand CF is stronger and stiffer by weight, but the same weight of CF is a lot larger than steel.
For a boring bar, we are limited by the size we can fit into the hole and we are not worried about weight.
Pete.

 

[petertha]

As mentioned above, there are always tradeoffs. Most of the attributes that make CF 'good' are in very specific load orientations. CF is great in pure tension (on a relative weight basis where that is important) but less so in other orientations. The loads are what they are, so trick then becomes how to orient fiber layups or windings such that the loads are dissipated. That usually means more material, more chance for discontinuities in the overall layup & more complex curing conditions (vacuum, pressure, autoclave... etc). Usually failure in composites happens long before the native fiber ultimate strength, usually some combination of delamination or failure of the binder/adhesive.

There are some good comparative plots here that compare attributes of various materials
http://www-materials.eng.cam.ac.uk/mpsite/interactive_charts/strength-ductility/NS6Chart.html

 

[Bentwings]

I just got done investigating items you outlined. I’m thinking I really jumped the gun on this. CF machinining the insert pocket and threaded mount hole would be beyond practicality. Also the natural frequent might be way out of line even with careful building. Spending a whole day screwing around with a questionable fabricated part is just not real. I think I’ll just wait for my next SSI check and buy the selected tool and inserts. I have a tool grinder and various honing blocks that work fine. So I’ll just work on feeds and speeds to get what I need.

thanks for comments. Sometimes you just someone to toss a hair brain idea in the dumpster. I’m going to look at possibly improving my existing tech skills.

byron