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Jacking Bolts: In-House Soultion

Bolt cc pic

JACKING BOLTS-IN HOUSE SOLUTIONS

Jacking bolts can be purchased, or made in-house. Here are a few examples of some pusher types:

Jacking bolts pic 1

A C-clamp. Weld a nut or tapped block to the side of the C-clamp. The clamp can then be mounted to the frame of the machine. They can be made in many different configurations, and can be removed after the shaft alignment is completed.

A dowel type. The base can be drilled to accept a piece of rod, which has been drilled and tapped to accept a bolt. This can also be removed after the shaft alignment is completed, or left in place.

Jacking Bolts pic 2

A channel. Drill and tap a piece of channel of the machine frame, and use a bolt or threaded rod to move the motor.

Blog by Stan Riddle, Vibralign

THERMOGRAPHY : NOW JUST A PHONE AWAY!

Reduced cost Thermal Imaging has recently become available through various sources. Now available through smart phones on Amazon.com as a tool for the millwright/mechanic. There are several types available. The thermal images shown, indicate the highest and lowest temperatures in the electric motor frame when the photo was taken. The only heat in the machine is right where it should be… in the rotor/stator of the motor. Misalignment and improper lubrication are two of the typical failure causes that IR images would reveal. 

COUPLING TOLERANCES VS. SHAFT ALIGNMENT TOLERANCES. WHAT’S THE DIFFERENCE?

This question still comes up fairly often in our training classes. If you look at any of the coupling manufactures installation instructions there is a chart for the maximum allowable misalignment based on the coupling size. These tolerances are for the coupling, what about the machines the coupling connects?

Shaft alignment tolerances are more about increasing machinery health were as coupling tolerances are more about how much misalignment a coupling can handle before it fails. However, coupling manufactures do recognize the importance of good alignment as there is typically a note in the installation instructions stating “Proper alignment yields the longest service life”.

That being said, the coupling maximum allowable misalignment tolerances are too “loose” when compared to shaft alignment tolerances and are also based on the coupling size. Let’s say a facility has 20 different size machines all operating at 1800 RPM and the 20 machines all have different size couplings. That’s 20 different coupling tolerances the mechanics will need to remember. If said facility aligns to shaft alignment tolerances, which are based on RPM, they have one tolerance for all 1800 RPM machines.

The following coupling tolerances are taken from the installation instructions for an elastomeric insert style coupling and a grid style coupling. Different coupling manufactures tolerances may vary. Also the angular coupling tolerance listed on the instructions were given as a gap or face value at the coupling O.D. which  We  have converted to mils/1″ (1.0 mil = .001″).

Elastomeric Insert Coupling

Coupling diameteroffset(mils)angular (Mils/1”)
4”1517.5/1”
6”2517/1”
10”3217.5/1”

Grid Style Coupling

coupling diameteroffsetangular (mils/1”)
4”51.3/1”
6”101.7/1”
10”121.2/1”

Recommended shaft alignment tolerances are based on “acceptable” tolerances used by industry and should be used in place of coupling tolerances when no alignment tolerance is specified by a company’s engineering or reliability department. Examining the 1800 RPM “Shaft Alignment” tolerances in the table and comparing to the tolerances for the coupling sizes shown; the “Acceptable” Angular Misalignment is 0.7mils/1”. That is 25 times better than the elastomeric insert coupling tolerance and 1.7 to 2.4 times better than the grid style coupling tolerance. The “Acceptable” Offset shaft alignment tolerance for 1800 RPM is 4.0 mils. That is 3.75 to 8 times better than the elastomeric coupling tolerance and 1.3 to 3 times better than the grid style coupling tolerance.

The goal of precision shaft alignment is to make the rotational centerlines of the machines collinear when in operation. Doing so minimizes forces being transmitted across the coupling, even with elastomeric style couplings, which increases rotating equipment reliability as well coupling life. Our goal is to “Save the Machine”.

Blog by Brad Case, Vibralign

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