since vex rasied their prices, I was looking for cheeper alternatives and found that REV 1\2 hex shafts are half price of VEX ones.
Because I am from Israel shipping and taxes makes the diffrence even bigger.
I know very well the quality of VEX hex shafts but does some one have experience with REV and andymark?
You may also want to check out these options: http://findrobotparts.com/shafts/categories/82,83/tags/1169,1179
I have used AndyMark and Vex in the past and I don’t remember having any issues.
I have had very bad luck with the uniformity of Vex hex shafts - often the longer stuff will be ever so slightly bent, making it just THAT much more annoying to get it in your bearings.
Have used AndyMark’s many times with no complaints. That said, it is not anodized, nor does it have a center bore, and costs essentially the same as Vex’s and Online Metal’s 7075 (~$5 a foot). I have never used Rev’s, but given the price and that the web site does not give the grade, I’m pretty confident it is not 7075; the price is a bit higher than onlinemetal’s 6061-T6511 hex shaft.
Note - I have never used oninemetal’s aluminum hex shaft, but I have used their 1018 cold roll steel hex shaft to good effect on longer runs where stiffness was important. The only problem was that the ends were mushroomed a bit, likely due to shipping. After cutting off an inch or so, it fit AM & Vex hex bearings and hubs and pulleys just fine.
My team has used Andymarks hex shaft for a couple years now. Using the 7075 they sell if a lot better than the 6061 we bought once from McMaster.
We modified a hex shaft in 2017 to fit into a seat motor and we noticed a slight twist by the end of our first event from too much torque. We made more spares and swapped them out between events. Following our first event, we went through like 5 shafts an event it felt like. We tried doing stainless but destroyed the worm gear in the gearbox from the torque. We just had to keep replacing shafts throughout season to compete, monitoring twist. We learned later that the first set of hex shaft we ordered for our first event was from an order I got together containing AM 7075, the rest of the reason, the mentors ordered due to busy schedules and the students just saying we needed more. The mentors ordered from McMaster, which was 6061. I had a moment of realization after worlds that the tolerance was worse along with the strength it felt like, and that it wasn’t the same material. We made shafts using the 7075 for IRI and ran the entire event on 1 shaft.
Long story short: look at the alloy of material. Even if its cheaper, you may be compromising the strength drastically.
Don’t buy the longer stuff for longer jobs. It’s specified on the site that the straightness tolerances are a lot looser on the long shafts.
Personally I swear by ThunderHex shaft, even if you’re using regular hex bearings. ThunderHex shaft + bearings are the way to go ideally.
If you are buying from other vendors (other than AM / Rev / Vex), check the tolerances. Cheapo aluminum hex bar is going to have very different tolerances than precision ground hex shaft. You would ideally want something like .498-.500 hex; not .500 + .005 or whatever you get with just a hex bar.
Adding onto the tolerances thing:
Every aluminum hex bar I’ve bought that was advertised as 1/2" has arrived oversized, except for the Vex anodized kind and the Andymark kind. I did have a bad run of AM shaft in 2014 that was oversized that we had to file down.
Conversely, 1/2" steel hex that I’ve bought is consistently undersized by ~0.001", making it a good fit for hex bearings. If you have a local metal supplier, take a hex bearing with you and try it out on their hex. In a pinch, steel hex can serve as a replacement for aluminum when Vex goes out of stock.
This is going way back in the time machine (8-10 years ago :yikes: ), but when I was a student I remember hex coming both loose and tight. The hex we used (used for live axles on press-fit AM hubs and performance wheels) was IIRC made by Kaiser Aluminum (who was a team sponsor). The tight stuff needed filing down to press in the hubs. The loose shafts were dealt with using sawed/lathe cut PVC spacers. Not a pretty solution, but it got the job done.
The longest shaft I remember was a 10-12" long drive shaft for a CIM-driven shooter wheel (2009), and it had significant vibration issues. We solved that by using some of the school shop’s steel hex stock normally used for making hand-forged chisels (read: not precision ground stock!). Was the vibration due to the Al flexing under load or the Al being bowed I can’t say. All I know was the steel shaft was a night and day difference and what was used for the competition season (and scored 1747’s first event win ever! ).
The other shafts were 6-8" running at a much lower RPM… there no issues that I recall other than the aforementioned inconstant stock sizes.
On this topic, are there any comparisons to which shafts have the least slop in 1/2" hex bores? Curious if there is variation between suppliers in that regard.
Depends on the 1/2" hex bore. Are concerned about bearings? Or plastic wheel hubs? Or maybe holes you make with a broach? They are not all the same.
My bad, should have clarified. More referring to gears and sprockets and hubs that we buy from common suppliers.
This is hard to answer based only on vendor drawings. Vexpro drawings show nominal 0.50 inch dimensions, although they do show 12.8mm (=0.5039") for Thunderhex and 12.7mm (=0.5000") for regular hex. Andymark shows 0.496-0.499" for their 7075 hex shaft. Both vendors show oversized hex bores in their gears; Vexpro has 0.503" nominal and Andymark 0.501-0.505". Adding all this up --> most of the time hex bore parts slide right on to hex shafts.
In my experience Thunderhex is often a little tight, and that is easily remedied with some light sanding. Either Andymark or Vexpro regular hex shafts are a bit looser than Thunderhex. This can cause a noticeable lash, but not as much as incorrect gear mesh C-C spacing.
As others have noted, in past years there have been a few oversize hex stock runs at both vendors. I have not seen that issue for some time now, though.
We’ve been buying 7075-T7351 1/2 hex from online metals for several years. We have a local warehouse; and normally pick up a several six or eight foot lengths before build season. Fits standard bearings very well with no issues.
Keeping the long lengths around, and simply cutting just what you need on the cold saw is really convenient. We have a full size lathe and tooling to produce any custom shafts; so we have zero interest in thunder-hex. Lightly breaking the edges at the shaft ends really makes it much easier to install the shafting through multiple bearings.
This still varies! Depending on the product.
Vex gear and sprocket hex bores are oversized in order to fit on these aforementioned oversized aluminum hex shafts without issue. The consequence is slop.
If you’re fine with a couple thou of variance, and slop is truly the utmost of concerns, I suppose you could start buying poorly toleranced hex stock and using the stuff that comes in oversized, for a better fit on those gears at the expense of the bearings. You could get a similar result by shimming the shafts, though.
In terms of things to optimize, though, optimizing for near-zero slop in all of your mechanisms is pretty far down the priority list. It can help with precise control of mechanisms with multiple stages of reduction and alternating loads that result in the mechanism “switching sides” of the slop (eg long arms going over center), but it’s definitely a top-1% kind of optimization.
Does a spreadsheet exist comparing AndyMark, Rev, VEXpro, & other FRC suppliers parts & prices ?
Not exactly what you’re looking for, but this site does a really good job of compiling sources for many of the typical COTS parts used by FRC teams.