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Info Letter No. 112 - Nov./Dec. 2008

by Fritz Ruoss


ZAR1+ Input Cutting Tool (Reference Profile)

Input window for tool profile dimensions was made more clear and easy. If not checked "Protuberance" and "chamfer", only required input fields for addendum, dedendum and fillet radius are displayed. Root fillet radius of tool can be entered only if no chamfer defined. Another new feature are the suggest buttons for default input. A mouse click into "<" at fillet radius raP0/mn calculates maximum tooth fillet radius. Remember that addendum of tool generates dedendum of tooth and vice versa.


ZAR1+ Input Generated Addendum Modification Factors instead of Flank Tolerances

Flank clearance is generated by tooth-thickness tolerances Asne and Asni. If you create a new gear, simply select tolerance classes to DIN 3967, and ZAR1+ sets Asne and Asni accordingly.

If you have to calculate a gear with unknown tooth thickness tolerances, you could use minimum and maximum over-pin-diameter to calculate generated addendum modification coefficients by means of our ZARXE software.

New Version 17.0 of ZAR1+ allows to switch input fields between tooth thickness tolerance and generated addendum modification coefficients. Relation between Asn and xe:

xe min = x + Asni / (2 * tan(al) * mn)

xe max = x + Asne / (2 * tan(al) * mn)


ZAR1+ Input Generated Addendum Modification Factors instead of Flank Tolerances

Button "^" has same function than selecting ".." at "Tooth thickness tolerance class Tsn". Input fields Asne and Asni are enabled then. Now you can click the button "Asn <-> xe" to switch to input of generated modification coefficients.


ZAR3+ Input Generated Addendum Modification Factors instead of Flank Tolerances

Similar than in ZAR1+, possibility for input of generated modification coefficients has been added to our worm gear software ZAR3+.


SR1 - Slotted Cheese Head Screw Form 1 and Form 2 Integrated

Slotted cheese head screw form 1 and form 2 were integrated into one database. Field "TYPE" defines Form 1 or 2.


SR1 - Surface Pressure between Clamping Plates

According to VDI 2230:2003, clamping area for washers has to be calculated with external diameter dwa = dw + 1,6 * hs (hs = washer height.

SR1 now considers this rule for the case that dwa is lower than the calculated value of the reference cylinder for calculation of elastic resilience. External diameters for calculation of surface pressure are now listed in printout under "de pmax". Maximum surface pressure pmax was renamed into "pBmax" (for maximum operating load FM+FSA according to VDI2230:2003).

pBmax = (FM,max+FSA) / Apmin

with Apmin = (de pmax - dh) *pi/4


SR1 - Tightening Torque of Countersunk Screws

Influence of head friction is higher for countersunk screws than for bolts with cylindrical head. Average friction diameter is calculated as follows:

for cylindrical head bolts: DKM = (DW+DI)/2

for conical head countersunk bolts: DKM = 1/sin(gamma) * (DA+DI)/2
(gamma = cone angle/2)

for countersunk screws with 90 cone angle: gamma=45
DKM = (DA+DI)/SQRT(2)

SR1 - Clamping Plate with Countersink for Screw Head

For clamping plates with counterbore for a hexagon socket head bolt, you must reduce length of the first clamping plate by height of countersink.

The same for countersunk screws, although in this case a part of the head height might be considered for calculation of elastic resilience. But it seems that, until now, no study exits for this case. Until then, SR1 calculates elastic resilience of countersunk screws equal than for cylindrical head bolts. For countersunk screw connections with short clamping length, please consider that elastic resilience may be higher than calculated by SR1.


SR1 - Slotted Countersunk Screws and Slotted Raised Countersunk Screws

ISO 2009 dimensions have been added to slotted countersunk screw database.

ISO 2010 dimensions have been added to slotted raised countersunk screw database.

And drawings of connections with countersunk screws have been improved, thread length sometimes was not displayed correct for this screw type.


SR1 - Hexagon Socket Countersunk Head Screw

Hexagon Socket Countersunk Head Screws according to ISO 10642 are new in SR1, size M3 until M20 can be selected from database.


FED3+ Tolerance for Bending Radius of Cranked Leg

For torsion springs with cranked legs, tolerance for bending radius was not displayed correct: tolerance for bending radius is defined in + direction only (not +/-).


FED3+ Tolerance for Bending Angle

At "Edit->Tolerance", you now can define also tolerance for bending angle or quality grade for bending angle according to DIN 2194.


FED3+ Bending Radius

If you define bent leg with bending radius smaller than wire diameter d, you get an error message (r < d). New version generates a warning even if bending radius r < 1.5 d. If you do not wish this warning, you can suppress it at "Edit->Calculation Method".

If you click suggest button "<", FED3+ sets bending radius r = 2 * d.


FED9 Stress Concentration Coefficient kb

Calculation of stress concentration factor kb was not exact for some cases and had to be corrected. Formula for stress concentration coefficient:

kb =  0,49 * t / r + 1.02

Stress concentration coefficient kb has to be applied if inner side of bent areas is stressed by tension. This is the case for dynamic stress or for load in opening sense of the spiral spring (negative spring angle).

If spring ends are cranked, load in closing sense generates load on the bended spring end in opening sense and kb has to be considered.


Short File Names for IGES files

IGES files are text files with maximum 80 signs per line. If file name with path is longer than 80 signs, this causes problems because file name is listed in the header of the IGES file. Since Nov.2008, only file name without path is listed to avoid this problem.

If you generate IGES files, pay attention that the file name is not too long. For older versions, also path should be short to avoid overrun problems.


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