Long reach attachments for drills, screwdrivers etc. secured by Trib-Joints made with a Trib-Tool™ 

Application Note 11. 

The securing of boring bars into tool holders and tools into extensions often involves messy and difficult brazing. TRIB-JOINTS™ are a simple press fit cold welding alternative.

Trib-Joints are Asperity Welds made with a TRIB-TOOL™ - a tool that dipenses trace amounts of Cold Welding Agent when it is trapped between the rubbing surfaces of two interfering parts as they are forced together - like a hard drill forced into the hollowed end of a softer steel extension bar.

In the case of drills, taps, screw-driver tips, hexagon keys or ring spanners - push together Trib-Joints that are stronger than the extension bar in torsion are easily formed by simply forcing press fit parts one into the other after treatment with a Trib-Tool. For larger parts making press fit Trib-Joints becomes progressively more difficult and pre-assembly by heat shrinking to trap the cold welding agent between the parts is more practical. During or after heat shrinking the joint needs to be slipped by a few degrees to activate the Cold Welding Agent and establish asperity welds within the joint. Alternatively the slipping can be affected under torque test or upon application of its first load, when after a few degrees slip the joint strength will typically double. The boring bars and drills may be either steel or solid carbide. It is essential that black oxide is abraded off the areas to be welded but it can beneficially be left on guide areas.

As an example a 25mm tool steel boring bar was cold pressed into a tool holder. The bar sheared in spiral fracture during torque tests at just above 900 Nm - proving the Trib-Joint, which was calculated to have a strength in excess of 2000Nm. - was substantially stronger than the tool bar. The retention of a Tungsten carbide boring bar into a hard steel tool holder more than doubled with a Trib-Joint over a heat shrink.

Sectioned view above of tool holder showing tool bar secured with a Trib-Joint. The bar was an ISO H7/p6 interfering fit (US class 7). The bar was treated as shown crosshatched, with the end left clean and dry. The untreated end acts as a guide to ensure the bar maintains axial alignment as the joint is formed. Only the bar was treated and then pushed fully in as shown. The Trib-Joined area is shown hatched.

Sectioned view of the coupling between a ground down drill and extension. Similar pre fits are used as above but the coupling can be allowed to expand plastically so pre-sizing is less critical - save for it must be an interfering pre fit, since asperity welds can only occur between contacting asperities ! The parts were pre treated with a Trib-Tool on the cross hatched areas on the shafts, so the untreated areas provide a natural guide during joint formation. They may be trued up parallel after assembly if needed.

for more information email: info8@tribtech.com

The TribTech name derives from "tribos" - Greek for 'rubbing'. 'TribTech' is a trade name used by Ball Burnishing Machine Tools Ltd. of 12 Brookmans Av. Hatfield, Herts. AL9 7QJ. United Kingdom;  Company Reg. No. 1408807, VAT Reg. No. 421 6210 04; a knowledge based company that develops, patents and licenses technology. All rights reserved by Ball Burnishing Machine Tools Ltd. Last modified: May 01, 2008 copyright © 1999/2008. The information and data provided herein should be considered generally representative for the tools and technologies described. In all cases users should carefully evaluate the tools and technologies to determine their suitability for a particular purpose.