Determining a Pinch Roller diameter

This page is to illustrate and hopefully help you determine the correct size

pinch roller for your reel to reel.  The first picture is a typical unit showing

the pinch roller on the machine.    I realize most  roller / capstan areas are not

this easy to get at,  but I used this one for clearity.  This roller comes

off by unscrewing the center metal cover.  Yours may vary.

  Step #1                                

First remove the pinch roller as showned in Picture #2  It is hard to see the

pinch roller shaft  in this picture as it is sticking straight up toward the camera.

                                                   

                                                                        Picture #2

Next measure the distance between the Pinch roller shaft and the capstan shaft.  

(Picture #3)The recorder selector handle must be in the play mode.  If your unit

is push button, plug it in and then push play. The pinch roller  shaft will move

forward as  if it was playing.  

Take that measurment multiply times 2

             

      Step # 2                                     

                                             

                                                                                         Picture #3

Distance between the 2 shafts = .538

                                  times               2

                                      ----------------

                                                  1.076

                                                

Now measure the diameter of the Pinch roller shaft  ,  as in the picture above.  

Add that diminsion to the total in step #2.

                     Example

                                                      Shaft diameter   =    .232

                  Distance between 2 shafts times 2   =   1.076

                                                                                                    ---------------------

                                                                           1.308

  This is the last and final step

OK ,   If I made the pinch roller a diameter of 1.308,  it is only big enough to

barely touch the capstan shaft, and there would be no pressure against the tape.

  So we have to give it some crush or pressure against the shaft to hold the tape.  

 Take the 1.308 and add  .125 to it,  that equals  1/8 inch to the total diamater

or 1/16 of an inch on each side,  you will now have 1/16 inch crush, or pressure

against the capstan shaft.   The  .125 is not an exact number.  It can vary  plus or

minus .015.

                                    Total from  above   =        1.308

                             Amount of total crush    =          .125

                                                                                                                 -----------------

        This is the approximate diameter the                       1.433

        roller should be  to fit your machine.  

                                                         

      Home