presto 45 speed adapter

[rsimms3]

That won't work for the K series since they are rim driven. The only ways to change speed for them is to add an adapter over the 33rpm pulley, make the tire on the outside of the rim smaller, machine a completely new pulley to replace the 33rpm pulley, or use a device that changes the speed of the motor up from 1800. The K series adapters had wings on them that put pressure on the larger section of the pulley (it never touched the rim so it wasn't an issue to scratch it) to keep it from spinning when engaged. Best method would be to machine something like what is in the picture below, but instead of wings make it a solid circle and thick enough for a set screw. I don't remember the spacing in the K series so I don't know if this is possible.

KSeries.png

[Jccc]

the picture of that 45 adaptor looks like it would work for the k8.

i guess its just a matter of knowing the diameter of it.

[rsimms3]

Yes it will, it's from the 45 adapter manual I mentioned. It doesn't indicate the diameter though, you'll have to do some calculations for that.

[piaptk]

I have always put the 45 adapters on with the plate down (how they were intended), but I bought a 6n that had one installed upside down with the plate UP, and a screw into the motor capstan to hold it in place... A brilliant and easy fix that I can't believe I didn't think of. You can get 6n adapters from Kim Gutzke (customrecords.com) for a reasonable price.

As far as k8s, you should have Rolandjays make you one. Give him the outer diameter of the current capstan and it is easy math to figure out the necessary outer diameter of the adapter. I'd buy a couple of those myself. I need to get him to make me some new 6n motor cap stand that have the 78 step of the capstan files down to 45 rpm so I can stop using the old school adapters.

[Snakeheadfishlab]

I would be interested in getting one for the k8 rolandjays.


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[grooveguy]

Hey, guys,

Isn't the K8 one of those recorders with a rubber tire around the outside of the turntable, and the motor shaft simply presses against it? It's kind of a horrible (and noisy!) way to couple the motor, but Presto did this on a number of machines, including their "Y" professional recorder.

As I recall from high school (please cut me some slack, this was 1957 or so) we had a K8 that actually did a quite good job cutting 78s for the girls' PE dance classes. Seems to me that the motor shaft had a pin going through it that engaged a slot in the bushing that went over the motor shaft to spin the turntable at 78 r.p.m.

You can get pretty close by measuring the motor shaft diameter with a micrometer or dial caliper, and then multiplying that by 1.35 to get from 33-1/3 to 45 r.p.m. BUT... that's not going to be exact because the smaller diameter shaft deforms the rubber rim differently from a larger one for 45 or 78.26.

How about wrapping Scotch tape around the motor shaft until a stroboscope disc indicates that you're right on speed, and then get a bushing machined for that diameter? I did this on my old General Industries recording deck in the even-earlier 1950s, and it worked fine. GI did finally come out with a 45 adapter, which was a wire-coil spring that you pushed over the motor shaft. The spring was wound with wire of a diameter that hit 45 r.p.m. right on the nose. You might be able to do something like this with the Presto, too.

[yourbedhead]

I would like one of these as well. Are you still interested in making them?

I can make you one . do you have any dimensions?
ill make a bunch and split the order between all the users .

[ROLANDJAYS]

ya ill make em .
how many are we talking ? 5? 10?
comment below and lets put out some dimensions to work from
thanks

[Jccc]

count me in on a k8 45 adaptor.

i do not know what the diameter if it would be tho

[rsimms3]

Use the math I posted on the previous page to determine the size of the adapter you want to have made. You can determine the diameter of your platter with the rubber on it by measuring your standard capstan if it runs true at 33rpm and making the platter diameter the variable.

[grooveguy]

The mechanical (spindle adapter) method of speed change is certainly the simplest, but unless you are a machinist, or are good friends with one, it can be expensive and maybe hit or miss. Years ago I had a Universal portable lathe that ran 33-1/3 r.p.m. only. The drive pulley was about 5 inches across and ran off a worm drive from the motor at about 100 r.p.m. Not an easy matter to change the pulley, so I made a motor-drive amplifier instead. A wein-bridge sine/cosine generator drove two amps that fed the two motor windings directly (no phase-splitting capacitor required); 60Hz for 33-1/3, 81Hz for 45. Each amp was about 40 watts and the whole thing was much easier, for me at any rate, than getting a new pulley made and dealing with a different size belt. Same could go for a Fairchild or other lathe that's gear driven. Today I'd use one of those Dayton Class-D 60 watts/chan stereo amps and a couple of hefty 25V filament transformers to get 120V out. I'm kind of a mechanical klutz, but electronics comes easy.

[markrob]

It is based on diameter, I usually use radius x 2 because it's easier to measure center to edge. Measure your platter for it's diameter. Then use this calculator:

http://www.culvermotor.com/Engineering-Formulas/Pulley-and-RPM-Calculator.html

RPM1 - Diameter1
RPM2 - Diameter2

RPM1 = speed of motor (1800rpm)
Diameter = X (size of new 45 rpm adapter)

RPM2 = 45
Diameter2 = Platter Diameter

Using the calculator above, Diameter1 will be selected as the X to solve for with your other variables entered. Hit the button and you have your answer. This number should be between the size of the spindle adapter and the 78rpm adapter. If it's not, then I've mismatched the variables.

That approach should work. It may be easier to use a micrometer to measure the current motor pulley shaft diameter (which produces the 78 RPM speed) and calculate the needed diameter based on the ratio of the two speeds (45/78). That would imply an decrease of .577 times the measured diameter to slow the platter down to 45. This method eliminates any error in measurement of the platter (not so easy to to do). One thing I noticed when I made a an similar adapter for a 6N I used to have was that the calculated numbers don't quite work out due to the deformation of the idler wheel. In theory, the diameter of the idler should have no effect on the speed, but in reality, it does have a slight effect as you apply pressure to engage it. Also note that the part needs to be carefully machined so that there is no eccentricity as this will case wow/flutter.

Mark

[Gridlock]

33rpm - 6.35 mm. , 45rpm - 8.65 mm. , 78rpm - 1.5 cm ...... This might be wrong. But it might be right. I think its wrong

[grooveguy]

Again, I might advise wrapping layers of Scotch 'Magic' tape around the 33-1/3 spindle until a stroboscope disc indicated accurate 45 speed. Then use a micrometer to _gently_ (don't compress the tape!) measure the new diameter. With the Presto outside rubber-tire drive recorders this would take deformation of the tire into consideration.

[yourbedhead]

Anyone have any luck with any of this?

[rsimms3]

It is based on diameter, I usually use radius x 2 because it's easier to measure center to edge. Measure your platter for it's diameter. Then use this calculator:

http://www.culvermotor.com/Engineering-Formulas/Pulley-and-RPM-Calculator.html

RPM1 - Diameter1
RPM2 - Diameter2

RPM1 = speed of motor (1800rpm)
Diameter = X (size of new 45 rpm adapter)

RPM2 = 45
Diameter2 = Platter Diameter

Using the calculator above, Diameter1 will be selected as the X to solve for with your other variables entered. Hit the button and you have your answer. This number should be between the size of the spindle adapter and the 78rpm adapter. If it's not, then I've mismatched the variables.

That approach should work. It may be easier to use a micrometer to measure the current motor pulley shaft diameter (which produces the 78 RPM speed) and calculate the needed diameter based on the ratio of the two speeds (45/78). That would imply an decrease of .577 times the measured diameter to slow the platter down to 45. This method eliminates any error in measurement of the platter (not so easy to to do). One thing I noticed when I made a an similar adapter for a 6N I used to have was that the calculated numbers don't quite work out due to the deformation of the idler wheel. In theory, the diameter of the idler should have no effect on the speed, but in reality, it does have a slight effect as you apply pressure to engage it. Also note that the part needs to be carefully machined so that there is no eccentricity as this will case wow/flutter.

Mark

The K8s have the same issue regarding speed variation depending on the amount of pressure applied. The post you quoted was older, I would do the calculations like you mentioned utilizing the size of the standard capstan and the 78 adapter to determine what the diameter of the platter should be with the rubber but ultimately your method would yield the most accurate sizing.

I had the same issue you did when having a replacement capstan made for my 6N, just slightly off and it sounds like a car tire with a knot on it.

[mischmerz]

I was thinking - wouldn't it make sense to get one of those .....

http://www.ebay.com/itm/New-Lesson-Speedmaster-174920-Adjustable-Speed-AC-Motor-Control-1HP-400-480V-/222098865498?hash=item33b61fbd5a:g:YwkAAOSwKfVXH5vL

... inverter motor controls? That might even allow cutting at half- and in between speeds?

Michaela

[grooveguy]

Hey, there you go! This Leeson thing is, in one compact box, what I described doing at great expense and gnashing of teeth many years ago in my post here on the 26th.. The advertised device is a 3-phase controller, which may or may not be what's needed to drive a fractional-horsepower hysteresis-synchronous motor, but I'll bet it could be made to work just fine with a bit of fiddling. Certainly the elegant solution, particularly on lathes with gear-driven turntables that can't be modified with spindle bushings. Good catch, Michaela!

[rsimms3]

I was thinking - wouldn't it make sense to get one of those .....

http://www.ebay.com/itm/New-Lesson-Speedmaster-174920-Adjustable-Speed-AC-Motor-Control-1HP-400-480V-/222098865498?hash=item33b61fbd5a:g:YwkAAOSwKfVXH5vL

... inverter motor controls? That might even allow cutting at half- and in between speeds?

Michaela

I think using a VFD would be overkill on a K8 for a couple reasons:
1. You'll have to run a separate power line for the motor since it currently is wired to/through the amp on a K8.
2. You'll have to find the correct VFD with single phase in/out as well as one that has the correct voltages on each side (assuming 120v on each side). I've been looking at them for my 6D, they aren't cheap. Single to three phase can be found fairly cheap, most usually run 400-480v out.

It would be a lot cheaper and less tedious to have the correct 45rpm adapter made to address it mechanically than electrically.

[yourbedhead]

I agree, now we just need someone that can machine us one...?

I was thinking - wouldn't it make sense to get one of those .....

http://www.ebay.com/itm/New-Lesson-Speedmaster-174920-Adjustable-Speed-AC-Motor-Control-1HP-400-480V-/222098865498?hash=item33b61fbd5a:g:YwkAAOSwKfVXH5vL

... inverter motor controls? That might even allow cutting at half- and in between speeds?

Michaela

I think using a VFD would be overkill on a K8 for a couple reasons:
1. You'll have to run a separate power line for the motor since it currently is wired to/through the amp on a K8.
2. You'll have to find the correct VFD with single phase in/out as well as one that has the correct voltages on each side (assuming 120v on each side). I've been looking at them for my 6D, they aren't cheap. Single to three phase can be found fairly cheap, most usually run 400-480v out.

It would be a lot cheaper and less tedious to have the correct 45rpm adapter made to address it mechanically than electrically.