1981Eagle Posted November 25, 2016 Share Posted November 25, 2016 I make a lot of things ... and I seldom do any 'plans' or work from prints. Typically - I look around at various designs and I mull things over in my head (often laying in bed not sleeping) and then - if is is a fairly complex project and I haven't worked it all out yet - I will make a mock-up in wood. I actually put more work than needed into the wood version. Here is a set of three long-range rifle bench-rests I made and the wooden one shown too. I got busy on my mock-up in wood for my 2x72 sander. Here's where I am so far. Working in wood is faster, I have lots of scrap lumber lying about, and it helps me work out how it will all work out and what metal I need to order. The main beam (the notched 2x6) is going to be 2x2 steel tube with a .120" wall. Hope you like it Quote Link to comment Share on other sites More sharing options...
JHCC Posted November 25, 2016 Share Posted November 25, 2016 So, the Y-shaped arm pivots to bring forward either the paten or the large contact wheel? Quote Link to comment Share on other sites More sharing options...
1981Eagle Posted November 25, 2016 Author Share Posted November 25, 2016 Yeah - but I had to work out where the pivot point needed to be so that the belt tension would be about the same no matter which one was 'out' I still a have to make a 'backing plate' behind the belt and a rest (for both sides) The motor set-up will be a 1-1/2 HP three speed stepped pulley Quote Link to comment Share on other sites More sharing options...
Steve Sells Posted November 25, 2016 Share Posted November 25, 2016 speaking of belt tension : how will you keep that ? as the belt stretches.. as you change grit/brands? and how will you change belts then there is tracking Quote Link to comment Share on other sites More sharing options...
1981Eagle Posted November 26, 2016 Author Share Posted November 26, 2016 The two wooden 'struts' will be replaced with gas struts - so that should take care of uniform tension. The top idler will have a tracking mechanism too ... probably a 'hinge' of some sort with a handle that allows me to pull the gas struts down and applies or reduces tension on the 'hinge' allowing for tracking adjustment. A couple things I didn't fashion out of wood - too intircate and I have a pretty good idea in my head of what I will do. Quote Link to comment Share on other sites More sharing options...
1981Eagle Posted November 26, 2016 Author Share Posted November 26, 2016 A lot of work - and a lot of left over 'scrap' that is going to be quite usable - and the platen/wheel armature is 'done' with the notable exception of a backing plate behind the belt and the rests for both. It is 5/8" 6061 AL - I figure it will be plenty strong enough for this application. Quote Link to comment Share on other sites More sharing options...
1981Eagle Posted December 1, 2016 Author Share Posted December 1, 2016 I got my first order of metal. The main beam is 2"x2" and I put it at a 12 degree angle. I have two 30lb gas struts on the way for a tension arm. Left to do is the tension arm with tracking control. Then the motor mount and drive-belt tension control. Then a bunch of finish work and paint and it's ready to use. Quote Link to comment Share on other sites More sharing options...
John in Oly, WA Posted December 2, 2016 Share Posted December 2, 2016 Interesting design. Looking good so far! Quote Link to comment Share on other sites More sharing options...
1981Eagle Posted December 3, 2016 Author Share Posted December 3, 2016 23 hours ago, John in Oly, WA said: Interesting design. Looking good so far! Thanks John ... In keeping with the 'interesting design' concept, I went with dual gas shocks on a telescoping mount, rather than a hinged arm with springs or shocks. Now I will 'work out how I will make the idler wheel / tracking adjustment. I'm liking it so far ... some of my welds aren't pretty, but they are solid enough. Quote Link to comment Share on other sites More sharing options...
Kozzy Posted December 4, 2016 Share Posted December 4, 2016 One minor point not specifically addressing yours but for those who might also be considering "rolling their own". Those stepped pulleys on the motor and arbor can vary wildly in quality. The cheaper ones tend to be cast spelter or another pot metal and are often far out of round and wobble to a significant amount. Bores are commonly often not perfectly square and concentric. This can send vibrations into the rest of the system which can be annoying and problematic. If building, It's likely worth the extra cost to go with a machined pulley for these (often still cast but of iron). It runs up cost but is an order of magnitude better than the cheap cast versions. If cost is a factor and the cheaper stepped pulleys need to be used, don't settle for a bad one: Replace it, true it on a lathe (carefully) or whatever it takes to improve performance. You shouldn't settle for one which gives crappy service. This is a machine tool, not some old blower where such a thing wouldn't matter. Quote Link to comment Share on other sites More sharing options...
1981Eagle Posted December 4, 2016 Author Share Posted December 4, 2016 1 hour ago, Kozzy said: One minor point not specifically addressing yours but for those who might also be considering "rolling their own". Those stepped pulleys on the motor and arbor can vary wildly in quality. The cheaper ones tend to be cast spelter or another pot metal and are often far out of round and wobble to a significant amount. Bores are commonly often not perfectly square and concentric. This can send vibrations into the rest of the system which can be annoying and problematic. If building, It's likely worth the extra cost to go with a machined pulley for these (often still cast but of iron). It runs up cost but is an order of magnitude better than the cheap cast versions. If cost is a factor and the cheaper stepped pulleys need to be used, don't settle for a bad one: Replace it, true it on a lathe (carefully) or whatever it takes to improve performance. You shouldn't settle for one which gives crappy service. This is a machine tool, not some old blower where such a thing wouldn't matter. Great point - and mine are indeed cheaper cast stepped pulleys - if they create a problem, I will certainly upgrade them. I made significant progress today, no photos, but the idler/tracking wheel is on One thing how much tension one a belt is too much? Or is there such a thing as too tight? Mine 'twangs' like a bow-string and it has 60lbs of force on it I still have to make a backer for the belt for the platen - and a rest. Then a rest for the 6" contact wheel. Last is the motor mount. Then final finish work and paint. Quote Link to comment Share on other sites More sharing options...
Kozzy Posted December 4, 2016 Share Posted December 4, 2016 The answer to tension is "as little as possible". No, that's not what people like to hear but it's more realistic than a number. The motor especially, doesn't have bearings which like a heavy side load. Tensions beyond the minimum needed to produce adequate driving friction do nothing but wear bearings out faster than needed. So, I'd adjust with an eye toward minimum needed to not slip under actual test pressures and to keep the belt from "flapping" under low tension but no more. The belt and pulleys themselves can take significant tensions but it's a waste if all that tension you apply isn't actually doing anything specifically to drive the components and only wearing bearings/contact surfaces. I fight this same kind of thing daily on drives for industrial equipment we do--everyone wants to crank tensions (especially on chain drives) so they are fiddle-string tight. I've even seen chains/sprockets/bearings worn out in days which should have lasted for years because of this. You need to think backwards and seek the "loosest" that gets the job done instead. It's not about how MUCH tension is right, but how LITTLE tension is right. That will vary by machine and a little fiddling in operation usually gets you there. Quote Link to comment Share on other sites More sharing options...
JHCC Posted December 4, 2016 Share Posted December 4, 2016 Piggybacking on what Kozzy says above, remember that you don't need a tight tension on the belt to produce a consistent grinding surface (unlike, say, a bandsaw blade, which will deflect considerably if not sufficiently tensioned). The platen and contact wheel will do that for you. Quote Link to comment Share on other sites More sharing options...
1981Eagle Posted December 4, 2016 Author Share Posted December 4, 2016 Thanks - I'll take off one of the gas shocks and see if it works with 30 lbs Quote Link to comment Share on other sites More sharing options...
Kozzy Posted December 5, 2016 Share Posted December 5, 2016 Oops...I was so sidetracked with the pulleys that I missed the point that you were talking about sanding belt tension. Higher tensions on a belt can start affecting tracking ability of a crowned pulley. Up to a certain tension , the pulley is able to correct in the normal way (a belt will tend to climb to the high spot which hopefully is centered) but above that, the tension tends to overcome the climb so you lose that tracking. Because sanding belts are typically effectively inelastic, that break-over point can often be quite distinct...a tiny tweak too much on tension and tracking goes all haywire. I'm actually writing a long drawn-out paper on belt tracking and why crowns track...plus failure modes of tracking for work now for inelastic conveyor applications. Too much to go into here unless someone really wants to know the boring nuts and bolts of the subject. Quote Link to comment Share on other sites More sharing options...
aessinus Posted December 5, 2016 Share Posted December 5, 2016 1981Eagle , that is a slick elegant design. Nicely done! If you are able (work stuff) Kozzy , please do post your paper in blueprints or the member gallery or somewhere. Sounds like interesting reading I might recommend to a young engineer I know.... Quote Link to comment Share on other sites More sharing options...
1981Eagle Posted December 23, 2016 Author Share Posted December 23, 2016 It is just about finished - just a couple more little odds and ends. I'm happy with the way it came out. It's not mounted to the bench yet, I need to make sure that it is where I want it to be. I'll probably design another front arm that holds an 8" wheel on one side and has a 'small diameter' contact wheel fork on the other. If you look carefully in the background, you can see my lathe, mill, parts of the surface grinder, pedestal grinder, the corner of the sandblast cabinet ... so this tool rounds out the shop nicely. Quote Link to comment Share on other sites More sharing options...
John in Oly, WA Posted December 23, 2016 Share Posted December 23, 2016 Nicely fitted out! Looks a lot better than the one I built. Quote Link to comment Share on other sites More sharing options...
Steve Sells Posted December 24, 2016 Share Posted December 24, 2016 4 hours ago, John in Oly, WA said: Nicely fitted out! Looks a lot better than the one I built. I have to agree, there is much I would have done differently and therefore it would never have turned out as nice a this one great job Eagle Quote Link to comment Share on other sites More sharing options...
1981Eagle Posted December 24, 2016 Author Share Posted December 24, 2016 Thank you both! One choice I made early on, I could have had the machine 'low' and 'long' like it is ... or I could have brought the motor toward me, and raised the idler ... I don't know which is a better design - but my 'low' one, coupled with the rotating front, causes me to remove the angle aluminum 'backing plate' of the platen. So if you do one, you should design it so when the contact wheel is 'out' the entire platen is inside the belt! Live and learn Quote Link to comment Share on other sites More sharing options...
Buzzkill Posted December 24, 2016 Share Posted December 24, 2016 I hesitate to offer any suggestions since you build looks so much better than mine, but I guess I'll do it anyway. If you are using aluminum for your flat platen it won't be flat for very long - unless you were going to line it with glass or something like that. Also, depending on how you mounted your flat platen you may be able to shorten it some so the belt fits in the opening when using the contact wheel. A lot of machines do have a platen several inches shorter than the distance between the 2 wheels so that you have a place for some slack belt grinding above the platen without removing it. In general though it's a professional and well built looking machine that should serve you well. One other minor detail is you may want a guard or two in place. One to keep the debris from your motor, and another to limit how much of the stuff goes around the belt and comes back at you. Quote Link to comment Share on other sites More sharing options...
1981Eagle Posted December 24, 2016 Author Share Posted December 24, 2016 Good suggestions ... I'll likely change out the flat platten with steel, I just didn't have the correct size on hand. But it's good to get me started. Thanks for the nice comment. Quote Link to comment Share on other sites More sharing options...
ianinsa Posted December 25, 2016 Share Posted December 25, 2016 That is a nice looking machine! My only comment would be that Aluminium oxide is I poor choice for a belt ceramic belts will perform much better with less strain on your machine, your profile doesn't give your location but if you are able to source Trizac belts(from 3M) they are brilliant. Ian Quote Link to comment Share on other sites More sharing options...
Marc1 Posted December 25, 2016 Share Posted December 25, 2016 Wow, that is a relief ... Looking at the pictures, I was afraid you were going to use the wooden prototype ... ha ha. The final product is nice looking and sturdy. Does the belt stay in place? Quote Link to comment Share on other sites More sharing options...
John in Oly, WA Posted December 29, 2016 Share Posted December 29, 2016 If you have enough belt adjustment, you could just let it ride over (outside) the platen wheels - or looks like it would ride the bottom one anyway - when the contact wheel is being used. Then you wouldn't have to take the platen off anyway. Quote Link to comment Share on other sites More sharing options...
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