View Full Version : Bring Bar

01-24-2009, 08:22 PM
I am looking for a 1-1/2 or 1-3/4 Dia. boring bar 20 inches long. Also needs to hld tool steel. Or information on how to build one (right metal heat treat etc) Thanks from Bob Scott.

01-24-2009, 08:33 PM
Check your PM
There is a link to one that me be of use to you.

01-24-2009, 08:57 PM
They are easy to make out of cold roll steel.

01-24-2009, 09:42 PM
I know good bars are hardened or even a Tungsten alloy. I am going to machine Iconel 800 HT. I need a good bar, I think?

01-24-2009, 09:49 PM
Boring bars suffer from flex due to lack of stiffness far more than strength problems; hardening a boring bar keeps it from getting scarred up when you accidentally hit the bore w/ the bar rather than the cutter, but does not affect the stiffness.

This is why a range of boring bars is good - you always want the largest one that will fit into the raw bore.

- Bart

01-25-2009, 09:38 PM
Boring bars are hardened and heat treated to increase their rigidity as well as there resistance to chatter.

01-25-2009, 11:26 PM
Barts is correct on this "hardening a boring bar keeps it from getting scarred up when you accidentally hit the bore w/ the bar rather than the cutter, but does not affect the stiffness."

Harding a bar does not change its (E)=modules of elasticity which is about the same for all steels.

A solid carbide boring bar does however have a higher E and there for will work better than a steel bar with a carbide insert. Gary P. Hansen

01-25-2009, 11:52 PM
Oh boy... we had this discussion on here before. Hardening does, in fact, change the mechanical properties of the bar. The ability of a bar to resist deformation is impacted by its hardness, which may be changed be heat treating. (It is usually not appreciable, however ... i.e. the reason the bars are hardened is primarily to protect their surfaces, not for decreased deflection)


The multiplicity of definitions, and corresponding multiplicity of hardness measuring instruments, together with the lack of a fundamental definition, indicates that hardness may not be a fundamental property of a material, but rather a composite one including yield strength, work hardening, true tensile strength, modulus of elasticity, and others. ~ University of Maryland CALCE


Hardness covers several properties: resistance to deformation, resistance to friction and abrasion.

The well known correlation links hardness with tensile strength, while resistance to deformation is dependent on modulus of elasticity. The frictional resistance may be divided in two equally important parts: the chemical affinity of materials in contact, and the hardness itself.

So it is easy to understand that surface treatments modify frictional coefficients and behaviour of the parts in contact. The abrasion resistance is partially related to hardness (between 2 metallic parts in frictional contact, the less hard one will be the more rapidly worn), but experiments carried out at Centre de Recherches PECHINEY in Voreppe (CRV), with TABER test show that the correlation resistance against wear/ hardness presents some inversions [28]

A correlation may be established between hardness and some other material property such as tensile strength. Then the other property (such as strength) may be estimated based on hardness test results, which are much simpler to obtain. This correlation depends upon specific test data and cannot be extrapolated to include other materials not tested.

The yield strength in tension is about 1/3 of the hardness [29]. To find the ball park figure for the yield strength convert the hardness number to MPa (or psi ) and divide by 3. For example take the Vickers number, which has the dimension kg/mm2, and multiply by 10 to (approximately) convert it to /mm2 (=MPa) then divide by three.

For example: HV 300 corresponds to a Sigma-y of approximately 1000 MPa. An approximate relationship between the hardness and the tensile strength (of steel) is,

Where HB is the Brinnell Hardness of the material, as measured with a standard indenter and a 3000 kgf load.


[1] Ref: http://www.plint.co.uk/at2/leaflet/te76.htm [2] Ref: http://www.mee-inc.com/microhar.html [3] Ref. thttp://www.ccm.ecn.purdue.edu/tfd/testing_methods/nanoindentation.htm [4] Ref. CALCE [5] Ref. CALCE [6] Ref. http://www.bikepro.com/products/metals/hardness.html [7] Ref.:http://www.wargamer.org/GvA/background/hardness1.html http://www.bartleby.com/65/ha/hardness.html [8] Ref. CALCE [9] Ref.:http://www.steelmill.com/DICTIONARY/dom_desc_576_594.html [10] Ref.: http://www.britannica.com/bcom/eb/article/2/0,5716,212+1,00.html [11]Ref.:http://www.bikepro.com/products/metals/hardness.html [12] Ref. CALCE [13] Ref. CALCE [14] Ref. http://www.britannica.com/bcom/eb/article/8/0,5716,40048+1,00.html [15] Ref. http://isl-garnet.uah.edu/Composites/s.html#Shore hardness [16] Ref. for Fig. 5 and Fig. 6: http://www.matweb.com [17] Ref. http://www.airproducts.com/chemicals/17600/castp.html [18] Ref. http://www.minerals.net/resource/property/hardness.htm [19] Ref. http://www.britannica.com/bcom/eb/article/4/0,5716,54534+1+53205,00.html [20]Ref. http://www.users.skynet.be/gentec/thrmsel.htm(companies provide different hardness values for their different type of die attach products. [21]Ref. http://www.engmatsys.com/die.htm(companies provide different hardness values for their different type of die attach products) [22]Ref. http://www.dowcorning.com(companies provide different hardness values for their different type of die attach products) [23]Ref. http://www.matweb.com [24]Ref. http://www.matweb.com [25]Ref. http://www.dowcorning.com a: Ref. By Pecht Handbook of Electronic Package Design, 1991 [26] Ref. http://www.hardnesstesters.com/hardness_train3.htm [27] Ref. http://www.wargamer.org/GvA/background/hardness4.html [28] Ref. http://www.kimwin.com.my/inj_89.htm [29] Ref. http://www.efunda.com/forum/show_message.cfm?start=1&thread=4261&id=4358 [30] Ref. http://www.engineering.usu.edu/mae/faculty/thfronk/mae2060/chap6/sld033 [31] Ref. http://www.adtdl.army.mil/cgi-bin/atdl.dll/tc/9-237/Ch7.htm#tab7_1

Copyright 2001 by CALCE and the University of Maryland, All Rights Reserved"

01-26-2009, 12:01 AM
Yes, and after all is said and done the diameter of the bar has more to do with stiffness than hardening or carbide. As one poster said, use the biggest bar you can and change sizes as required. I have used inner tube rubber wraped on the bar to dampen it and hung a weight from the back side.

Sometimes there is nothing you can do to stop chatter.

01-26-2009, 12:05 AM
Absolutely! Not arguing against good sense :)

01-26-2009, 04:25 AM
The hardness of a steel bar (eg it's heat treatment) has almost nothing to do with its resistance to deflection - its stiffness. This property is represented by Young's Modulus, commonly denoted E. E does decrease with temperature,

A boring bar is essentially a cantilevered beam, and deflection, rather
than yield strength is the limiting constraint, since proper operation of the cutter and prevention of vibration, chatter, etc requires that cutter position be closely maintained.