MVII motor belt length

[n240sxle91]

Once again your knowledge of the Mark VII amazes me!

The belt I have is the "501330 DF". It appears to run the machine well, and I haven't had any problems with it in my very limited time with it. As you found it does increase the RPM slightly. My tach shows my slowest speed to be around 775 RPM. I'd prefer it get down to 700, but for now I can live with 775. I looked closer at my gear rack and I found another spot that shows wear. So, I absolutely agree with you that either an idler pulley needs to be installed, or at least a shield to protect the gear rack. The belt slap really is a design oversight, and I bet it probably would have been fixed had the Mark VII continued on longer.

[JPG]

I must give n240sxle91 credit for calling me out with the 29.5" belt he successfully installed. Since originally creating this thread, I have acquired a real MVII motor belt in new condition(unused). It measures 29.5" which I determined only last night.

BTW 29.5" is outer circumference.

[rpd]

A pop can sleeve increases the threaded 1/4-20 screw closer to bearing id of 7 mm and eliminates the thread bumpiness.

I know this is an old thread, I was just reading it again, researching belts, and the above line caught my eye,

For anyone making an idler pulley like this, an alternate solution to making a sleeve from pop can aluminum, would be to use a brass tube from a slimline pen kit. (they fit in a 7mm bore and slide onto the 1/4" mandrel) so in theory should be a good fit.

[JPG]

A pop can sleeve increases the threaded 1/4-20 screw closer to bearing id of 7 mm and eliminates the thread bumpiness.

I know this is an old thread, I was just reading it again, researching belts, and the above line caught my eye,

For anyone making an idler pulley like this, an alternate solution to making a sleeve from pop can aluminum, would be to use a brass tube from a slimline pen kit. (they fit in a 7mm bore and slide onto the 1/4" mandrel) so in theory should be a good fit.

Do you know what the tube wall thickness is? 0.012" seems thin????

I agree a brass tube is preferable to a rolled strip of pop can!

[n240sxle91]

Although, an idler pulley isn't necessary when using the correct sized belt. A simple gear rack shield is all that's needed now.

[rpd]

A pop can sleeve increases the threaded 1/4-20 screw closer to bearing id of 7 mm and eliminates the thread bumpiness.

I know this is an old thread, I was just reading it again, researching belts, and the above line caught my eye,

For anyone making an idler pulley like this, an alternate solution to making a sleeve from pop can aluminum, would be to use a brass tube from a slimline pen kit. (they fit in a 7mm bore and slide onto the 1/4" mandrel) so in theory should be a good fit.

Do you know what the tube wall thickness is? 0.012" seems thin????

I agree a brass tube is preferable to a rolled strip of pop can!

Ok. Home from work and measured a pen tube with my dial caliper. (the digital one always had a dead battery when I went to use it. )

OD - 0.266
ID - 0.248
Wall thickness - 0.009

I also tried a 1/4 - 20 and a 1/4 - 28 bolt and they both fit nicely.

[JPG]

Although, an idler pulley isn't necessary when using the correct sized belt. A simple gear rack shield is all that's needed now.

I think an idler pulley makes an excellent shield.

BTW WHERE does one get one of those correct sized belts? That includes the 17/32 width!

[n240sxle91]

Oh, absolutely it makes a good shield. It's just a lot more work to install. For someone who doesn't have one installed I'd recommend just making a shield to protect the gear rack from the small amount of fluttering the belt does.

You can get the belt off of Amazon for about $4.

D&D PowerDrive A27.5/4L295 V Belt, A/4L, Rubber, 1/2" x 29.5" OC https://www.amazon.com/dp/B00EOVLUOQ/re ... ZBb92VHR0J

[Mike]

Looking for the right belt and this was like reading a story with a happy ending. Thank you!