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UMO B&B Manufacturing 298MXL025G Replacement Long Belt Set Review

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Posted (edited) · UMO B&B Manufacturing 298MXL025G Replacement Long Belt Set Review

I suspect that more than a few members here may have older UMs with aging stretched belts and might benefit from my experiences with belt replacements.

I removed my short belt drive mechanisms and replaced them with direct drive over a year ago:


You can checkout the "Made" link in the above page for my photos and notes. After installing the direct drive components, my UM became quieter and it required virtually no belt adjustments. (I re-bent my clothespin spring adjusters once.) I've tried several cool-looking printed manual tensioners, but I prefer the self-adjusting long belt clothespin spring tensioners, barely ever require any manual adjustment or maintenance.

Almost immediately after assembling my new UMO over three years ago, I felt the supplied belts were a touch on the long side. After a short break-in period, the 3 mm screws and nuts in the belt "claws" of the slider blocks ran out of their extremely limited adjustment range. I suspect the screws and nuts were added by UM designers when they discovered that the claw did not result in sufficient tension of the 300 mm long belts and supplies of a slightly smaller belt size were problematic, due poor market availability. Regardless of the reasons for the 3 mm hardware, it is really a poor excuse for a belt tensioner!

Thus I ran perfectly satisfactory, but kludgy-looking, clothespin springs for over three years. Recently, even bending the springs as much as possible, to maximize the tension of my aging belts, resulted in the springs rubbing gently on the UM's frame and still somewhat inadequate tension. (I could no longer "jump" reliably at 300 mm/sec!) I knew it was time to replace my long belts.

Rather than buying 300 mm replacements, I decided to special order 298 mm belts from B&B Manufacturing in the U.S.:


Unfortunately, BBMan charges some pretty hefty extra shipping and handling fees but also discounts quantity buy levels. Accordingly, I ordered 12 belts to more favorably amortize the $17.42 USD shipping and handling charges, which is an outrageous sum for an order quantity that fits in a medium size envelope! The total charges, delivered to my door about two months later, were $63.26 ($15.82 per long belt set), but now I probably have more than a lifetime supply of UMO belts!

The 298MXL belts are the perfect size for use without any extra 3 mm claw tensioner hardware. (The wooden claw part alone results in perfect tension.) The 298 belts were slightly more difficult to install than the original 300s, and they were on the tight, but still acceptable side, in a belt pitch tone test before break-in (I think tone is the best way to check UMO belt tension), but they are perfect after a couple of prints worth of break-in time:


(I don't know why UM doesn't emphasize the above method, because any belt tension evaluation that is based on belt deflection depends on providing a known and standard pull force on the belt!)

I expect to get maximum service life from these belts, because no extra tensioner is needed initially, as it was with my original UMO 300 mm belts. I'll probably add my clothespin springs again, when necessary, for set and forget convenience, but the original 3 mm claw hardware could also be used to extend my 298 mm belt service life beyond what it can accomplish in tensioning the original belts too.

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    Posted · UMO B&B Manufacturing 298MXL025G Replacement Long Belt Set Review

    Interesting video. I'm definitely going to look at my printers later tonight to check the tension.

    Thanks for sharing and for the possible replacement source.

    Did you look at replacing them with the original one from fbrc8?


    Would probably have been less expensive.

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    Posted (edited) · UMO B&B Manufacturing 298MXL025G Replacement Long Belt Set Review

    Did you look at replacing them with the original one from fbrc8?


    Yes--most definitely! I've purchased parts from fbrc8 and it is an excellent vendor. I was very pleased when fbrc8 got a contract with UM Ltd. to be a support partner in the USA.

    Yes--fbrc8 would have been cheaper in the short term, but I don't need the short belts in the set and assuming that I keep my UMO for a long time or another direct drive UMO mod'er needs only a set of long belts, I think the B&B belts will work out to be more economical in the long run. They fit better than the original belts initially and have more room to stretch with any given tensioner. They fit so well that, hopefully my machine will not need any belt tensioners at all for a long while.

    Also, I probably could have continued to use the old belts with some other type of manual adjuster that could take up more of the slack, but clothespin springs are my favorites. They are "set and forget" and they feature a fairly wide adjustment range too. However, I can think of a couple of non-spring adjusters that might be able to take-up even more belt slack.

    On the other hand, the tooth spacing is continually increasing when belts age and stretch, so maybe a new tensioner would not have re-enabled 300+ mm/sec jumps for me, which  helps with stringing and hairs in nylon prints.

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