This partial calculator evaluates maximum in-line slider-crank obliquity for selected dimensions, ideal transverse reaction under an entered axial slider load, entered rectangular projected area and arithmetic average pressure. It does not rate a form-4 guide, slipper, bearing, lubrication system or service life.
Steam Engine Guides Form 4 - Selected Ideal Load/Area Ledger
Explore selected ideal maximum obliquity, transverse reaction and projected-area arithmetic.
Equation Used
- Axial slider load, crank radius, rod length and projected rectangle dimensions are entered values.
- Rod length is constrained above the maximum selectable crank radius so L>r throughout the input domain.
- The connecting rod is treated as an ideal two-force member at maximum obliquity.
- Pressure is an arithmetic average over entered projected rectangular area.
- Contact, lubrication, thermal behavior, wear and safety are excluded.
The secondary figure is an abstract load/area ledger, not a form-4 guide design.
Selected ideal load/area ledger
For crank radius r and connecting-rod length L with L greater than r, maximum rod obliquity is arcsin(r/L). Under an ideal two-force-rod assumption, maximum transverse reaction magnitude is F tan(phi_max). Entered slipper length times width gives projected rectangular area, and reaction divided by that area gives an arithmetic average pressure.
What the calculator determines
Use it to inspect selected ideal geometry, force resolution and area arithmetic. It cannot determine actual loading history, contact distribution, oil-film condition, temperature, wear or allowable operation.
Selected relationships
phi_max=arcsin(r/L); F_trans=F tan(phi_max); A=l w; p_avg=F_trans/A.
Selected-input example
At axial slider load 18000 N, crank radius 100 mm, rod length 500 mm and entered projected rectangle 90 by 80 mm, maximum obliquity is about 11.537 degrees, ideal transverse reaction is about 3674 N, area is 7200 mm2 and arithmetic average pressure is about 0.510 N/mm2.
Not a guide or slipper rating
Changing axial load, inertia, friction, gravity, clearance, alignment, deformation, edge loading, material, surface finish, temperature, lubricant, oil supply, wear, impact and safety are excluded.
Questions
Why must rod length exceed crank radius?
That condition keeps the selected in-line slider-crank geometry real through the full cycle.
Is average pressure the peak contact pressure?
No. It assumes uniform distribution over the entered rectangular area.
Does the result validate a slipper?
No. It is selected ideal arithmetic only.
Authoritative references
- Penn State ME 581 slider-crank equations — gives phi=asin(R sin(theta)/L).
- NIST Guide to the SI, Chapter 4 — identifies pressure in Pa=N/m2.
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