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knurled press fits Question
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Posted by: dewan_piyush

05/04/2006, 14:06:29

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could anyone tell me about interference fits of pins having knurling...... or knurled press fits...how to calculate the amount of force tat should be applied etc. etc. ?







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Re: knurled press fits
Re: knurled press fits -- dewan_piyush Post Reply Top of thread Forum
Posted by: Kelly_Bramble

05/05/2006, 09:11:07

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The only time I have ever used a knurled diameter was for a threaded bushing in plastic, and the it was actually a vibration / heat install (not pressed).

The OD of the knurled pin is unlikely to be very close toleranced, and need a lead-in taper on the pin. With a strong enough press, designing your press fit hole to some number larger than the minor diameter of the knurl could work fine. I'm sure that the knurl pitch and depth could have a great effect on usability and press force required.

Why a press fit knurl? and what material? Keep in mind that this would be a one time installation design.







Modified by Kelly_Bramble at Fri, May 05, 2006, 09:12:35


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Re: Re: knurled press fits
Re: Re: knurled press fits -- Kelly_Bramble Post Reply Top of thread Forum
Posted by: randykimball
Barney
05/05/2006, 19:28:38

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I've used knurl to a press diameter several times over the years. However, everytime it was to save a part that had lost its fit because of repeated removal or to save a part that didn't have quite enough press fit. In none of these times did the knurl ever return the fit to its orginal fit function, but worked each time as a stop gap or emergency save.

One must remember that a knurl digs material out of the grooves and raises them onto the diamond shaped ridges.

During a press process if the materials are of aprox equal hardness the ridges are mostly going to be pushed back into the pockets.

If the non-knurled part is softer, then the knurl will push material ahead of it.

One place knurled diameters are good is when the female part is shrunk fit to the male portion. This makes a great connection.

In turning a mandrel for knurl to be pressed into a female part simply turn the male portion to the same press fit you would have without knurling. The knurl will add some grip. Knurl is a great way to cause parts made of gummy material to guald together, if you have no plans to ever seperate the pair.

Also, as Kelly stated, when you press a knurled part into a hole, you only get one try, it is ruined after that. There will be no press out and repress, it would be a press out and not be a press fit again.

However, a spline or straight knurl with a harder male portion in a press fit is an intirely different matter. It WORKS! WELL!..... one time...





The worst suggestion of your lifetime may be the catalyst to the grandest idea of the century, never let suggestions go unsaid nor fail to listen to them.

Modified by randykimball at Fri, May 05, 2006, 19:37:34


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