Can you describe exactly what moved?
Unfortunatelly my CnC was working fine milling wood so decided to cut aluminum ... and ....... went too deep at first cut.....
Let's just says now I have to take whole gantry apart and re-align it.
would be nice if it is solid piece so you don't have to wory about screws that can get loose ( well not loose but parts can still twist under preassure) ... and move parts.
will see if I can post some pics later
Can you describe exactly what moved?
The Carriage block went out of alignment ( not square anymore) ..... working on it to make it square again.
and actually I was using lock washers a lock nuts.
sounds like same issue I ran into, I posted in another thread I am building the carriage from a solid piece but this is close to impossible to do without a mill. This would be too much to attempt with handtools besides not cheap if you make a mistake. A chunk of aluminum that size costs about $250. Will post pics once I start machining the new carriage.
i think bob should offer a solution , may be a cross beam?
Don't get me wrong.I am suggesting a solution and hoping that bob will tell if solution is right or some Better solution as we know he know machine in and out.
What is Fault in cross beam.it can be attach to back by bolts that attch the berrings.
I think bob should offer a lot of things...i think bob should offer a solution , may be a cross beam?
First we need to asses if there is actually a problem that needs a solution. It sounds like the problem that billj had was related to the threadlocker not allowing the nuts to be tightened enough, and once a set of studs/bolts with adequate tightness were in place things were OK. And it sounds like fastpcuser ran into the problem when taking a really heavy cut in aluminum.
My sense is that the issue is simply one of making sure there is an adequate way of getting those four studs tight enough. Those four points are clamped moment connections that rely on the friction of the parts being bolted tightly together. So I've decided to empirically test this joint. I just ordered some aluminum stock to test exactly how many lb/ft of torque it requires to cause slippage of this type of joint. I'm planning on using two lengths of 3/4" square aluminum bar stock. I am going to put a 1/4" stud in one, a spacer as per the plans, and then a second bar oriented perpendicularly. That second bar will have some length to it. I'm going to clamp the first bar securely in a bench vise and apply a measurable force to the second one to see how much it takes to move the joint. I'll use a torque wrench to tighten down the nut that is on the stud so I can relate tightness of the nut to joint movement. I might test a few different variations of this- different stud diameters, bolt vs. stud, threaded vs. unthreaded spacer, etc. If this reveals that it takes less force than I am imagining to move the joint, then I'll come up with a solution. Ideally,one that can be retrofitted to any existing machines.
While I appreciate the suggestion of a cross beam, I think this is looking too narrowly at how to solve the "problem." Unless I am not understanding what you are envisioning (entirely possible without a drawing), any type of diagonal crossbracing won't help entirely. Unless there are two that work in opposing directions, and they could be tensioned to remove slack, there would be the problem of still allowing movement until bolts contacted the sides of the holes they went through. Any improvement to the existing design probably wants to create a positive interlocking of parts that no longer relies on friction joints at all.
I'd generally agree with this, but it would still be nice if slippage under heavy use didn't occur at a point where it is such a pain to realign things. Mistakes are inevitable, and something like an error in feedrate or depth of cut should have a predictable way of absorbing this force that isn't damaging or inconvenient.Why? Folks are using the machine beyond its intended performance. And it seems to perform fairly well at that.
But rest assured that I'm looking into the situation. I've had a few oops moments while cutting aluminum (like a brief 200 ipm cut) and haven't had this carriage slippage problem, so it came as a surprise when it happened to Bill. If there needs to be a solution, even if it is as simple as specifying a required torque wrench setting for those four nuts, it will happen.
p.s. fastpcuser, has the problem occurred again? Also, any pics of your completed machine?
right now everything is aligned and works good. This time I tightened all the bolts pretty good one of them I actually broke off by tightening it (had to replace it, but for my surprise I was able to unscrew it with hand tools even with threadlocker (red one).
sicne then I haven't tried aluminum yet, but tried plastic and wood everything seemed to be good.
will post some pics
Here are some pics...
Hey, the machine looks great! Nice to see another machine up and running. Time to give it another try with aluminum.
OK, I did some quick looking at some bolt data and it looks like the simplest upgrade would be to replace the 1/4-20 studs with 5/16" through-bolts. Switching from 1/4-20 hardware store grade (grade 2?) threaded rod to 5/16 grade 8 bolts would increase available axial clamping force by over 3.5 times. This would also avoid tapping 4 holes, and the worst that happens if you over tighten anything is a broken bolt, rather than a snapped stud. It looks like 2 1/2" long bolts (or 2 3/4" depending on your choice of washer configuration) run through from the front should fit OK and clear everything. Or you could do it the slick way like billj and use socket head cap screws sitting down in counterbores.
I'm still going to do some empirical testing of this joint, but this simple upgrade looks like it should do the trick and avoid most problems.
I would agree that is a sensable upgrade. If necessary. Also, one should have the parts clean before assembly. Anything that can act as a lubricant between the aluminum bars is a detriment.