Fits like a glove

“Fits like a glove” characterizes a carefully designed or measured correlation between two separate parts or components.  This union being depicted as a good or proper fit.  If these mating parts are designed to move, we will ultimately have what is known as wear.  Since wear exists, so does Machine Worx.  We deal with fits and wear on a daily basis.  This info-letter is designed to help give you a better understanding of the allowances and tolerances required for proper fits.  This will allow you to specify these different types of fits in order to meet your requirements.

Once wear has has deteriorated the proper fit, stresses are reallocated in the adjacent parts until failure ultimately occurs.  The deterioration process can sometimes be detected by an audio and/or visual inspection, but your most valuable source of wear detection is the machine operator.  Listen carefully and ask questions because the operator can provide valuable clues in locating the problem.   A golden mound of “bronze grease”, metal slivers in oil sumps, oblong holes and pins, new noises and vibration are all common signs of wear.  Once the problem has been found, you must determine the extent of wear deterioration.  This can be almost impossible if you do not know what the original fits were.  

Fits can be grouped into two different categories, “clearance” or “interference,” and we’ve included a basic quite for some of the “classics”:
FIT - COMMON TOLERANCE - CLASS

Bronze Bearing O.D.  -  .001/.005”  -  interference

Bronze Bearing I.D.  -  .001”/inch of dia.  -  clearance Slip Fit  -  .001/.010”  -  clearance Sliding Fit  -  .001/.002”  -  clearanceTap Fit  -  .0005/.001”  -  clearance Driving Fit  -  .000/.0005”  -  interference Press Fit  -  .001/.005”  -  interferenceShrink Fit  -  .004/.010”  -  interference Bearings  -  consult bearing manual  -  as required Throwing a Fit  -  none  -  interference

The above figures are merely guidelines as shown.  When calculating clearance or interference fits, the following factors must also be taken into consideration:
Function - what type of movement is required.Type of mating materials - cast iron/steel, steel/bronze, etc.Lubrication - oil, grease, automatic, submerged, etc.Weight - of the moving member.

Speed - of the moving member.

Size - of the moving member.

Percent of contact - example: a round pin in an oval hole.

Keep in mind that all of these factors play a significant part in determining the tolerance or allowance of the fit and can change the chart figures dramatically.  Once the primary function of the component has been determined, other factors such as “longer life”, “ease of replacement” or “cost of repair” should be considered before the final repair is made.  Sometimes new engineering techniques and higher quality steels can make repaired areas outlast original equipment.  Contact Cy or Jerry for ideas!  Remember: if you detect a wear problem, don’t throw a fit, call Machine Worx for a lasting fit engineered with longevity in mind.
Whether you need:parts repairedmachininga complete design and buildreplacement partsfabricatingadvice
Call Machine Worx.  We will be glad to serve your requirements with fabricating and machining that “fits like a glove.”

For over 135 years, Machine Worx has been serving the needs of industry.  We are dedicated to the quality minded professional who wants to fix it right.