Hi Martin

On these machines, the concept of the carbon copy adjustment wheel is to increase or decrease the speed of the drive roll thus giving the type bars greater or lesser velocity as they travel towards the platen. This is done via the variable intermediate pully on the two belt drive system. The electric motor is located at the back left corner of the machine and turns at a constant speed. The primary belt is driven via a centrifugal clutch for easier starting of the electric motor and drives the large diameter of the variable pulley.

The secondary belt is driven by the small diameter of the variable pulley and drives the drive roll under the keyboard. The center section of the intermediate drive pulley can slide side to side between the outer sheaves of the pulley, thus changing the effective diameter of the two grooves of the pulley. If you remove the ribbon cover or hood and turn the typewriter on, you should see these belts and pulley turning.

With the copy wheel set to 1, the center section of the pulley should be to the right making the primary belt sit high in the groove. As the copy wheel is moved through the various positions to 10, you should see the center section of the variable pulley move very slightly to the left. You should also notice the primary belt sinking a little deeper into its groove, the secondary belt climbing up out of its groove and the variable pulley spinning a little faster. Run this check and let us know what you find.

I have a copy of the SCM 6, 7, & 8 side loading cartridge ribbon electric typewriters and can scan the relevant pages if you think this would help. However, a level of technical knowledge is required to understand the manual and I wouldn't be able to scan them until Monday. When I first saw the dual belt drive system, I recognized it immediately as being the same concept as the variable speed drive for the threshing cylinder in a combine harvester. Having a mechanic's background definitely helps when it comes to understanding how these machines work. All the best,

Sky

Hi Again Martin

Although the side to side movement of the center section of the intermediate variable pully is barely discernable, if the primary belt is moving up and down in its groove as you turn the copy wheel, the variator is working correctly. Another possibility although very rare is the ring and cylinder getting out of adjustment. The ring refers to the semi circular band of metal just above the segment but below the type guide base plate and the cylinder refers to the platen.

To check this you will need a set of feeler gauges as used when setting the valves in an engine, select the .028" and the.040". With the ribbon cover off and the ribbon removed, run the motor and make note of which way the pulleys turn. Center the carriage and set the shift lock then turn the motor off. Press the H key and manually rotate the pulley to lift the H type bar off the type bar rest.. Lift the H bar up until it lightly rests on the ring to check the clearance between the type slug and the platen.

If the .028" feeler slips in between the platen and the type slug but the .040" does not, you are within specification. Your problem is most likely the rock hard platen. Try using a sheet of 32 lb. paper as a backing sheet and see if that makes a difference, some typists will use a sheet of construction or craft paper as a backing sheet. Getting a platen re-covered by J.J. Short can be a bit pricy, but is well worth the investment if the typewriter has some special significance. Another trick to try is to order in a sheet of 1/32" neoprene rubber sheeting from your local NAPA store for use as a backing sheet. This is about all I can suggest to you on this machine, maybe someone else might have a few other suggestions. All the best,

Sky

I had neglected to mention in my 1st post that this part about, 1 1/2 in, was loose in the bottom of the Coronet...It did not seem to go anywhere that I could see but since I have this strange issue with the Copy Set dial I wonder if it is a part that someone neglected to reinstall at some point.  Does it explain the bass-akward dial pressure and is it worth fixing?
https://imgur.com/a/fSURPIY

M.Hohne:  Wow if you are right that metal piece was rattling around inside the  typewriter, not in the case, for about 50 years!  Thanks for this explanation.  I would have always wondered if this typewriter was complete.