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View Full Version : Quick Q: Is ur leadscrew tight when turned by hand?



andyew
01-14-2005, 01:33 PM
Hi all,

Just a quickie question for u all:
- Did u find that when u try to spin or turn ur leadscrew on ur machine with hand (without motor mounted), it feels kinda tight but turnable???

I have this phenomenon for mine, not sure if it's abnormal or wat.... otherwise, it might be leadscrew-misaligned, delrin nut not lubricated, bearing not greased enuff or other possible causes!

Let me know ur situation, at least i know roughly what is considered NORMAL!

Thanks ya!
Andy

JavaDog
01-14-2005, 01:46 PM
On the assemblies I bought off of ebay (Screw and Rails) I can give it a spin with my hand and it will go for quite a few turns before stopping. Granted, there is very little load (no gantry or anything) mounted on it.

buscht
01-14-2005, 02:08 PM
Andy, If you have a ballscrew it should turn easily, two fingers should be able to move the carriage back and forth.
I'm not sure with an ACME thread lead screw.

Moondog
01-14-2005, 02:53 PM
Hello Andy...

An Acme thread leadscrew will not turn as easily as a Ballscrew. However there should be very little friction/resistance when turning by hand.

How are the ends of the screw mounted?....

Is the Lead Nut mounted to your slide (ie, Z axis).

Sounds like you have a binding problem and you need to determine where it is binding. Series of eliminations.

Firstly, disconnect your belt and any fittings to the Lead Nut. The lead screw should now just be held by your mountiings. Does it now turn freely. If so, you can assume that your bearings and alignment are correct.

Usually this sort of binding happens when you connect the Nut to the Axis assy... if that is not dead square and parrell it will bind.

Andy.. how is it mounted?... is it your Z,X or Y.. and the mountings????

cheers

andyew
01-16-2005, 02:31 AM
Thanks every kind person.....

Sorry for not explaining more details but i was afraid i would bore u guys with my story... anyway, i explain briefly my situation

I have the delrin nut tapped with the homemade ACME tap and it turns like a charm, almost not backlash detectable by hand and eyes + it turns very smoothly like Javadog has said... But when i mounted the delrin nut onto the moving base (where there're linear bearing slides on both sides), the BIG HEADACHE PROBLEM came in instantly. I hardly can turn my leadscrew like i did before mounting the gantry-base and linear bearings.

My linear bearings slide on the 2" sst pipe, where these pipes can be adjusted to compensate any misalignment.

One more thing, i've tried to lift the gantry-base up using my hand while my friend is turning the leadscrew, there's an OPTIMUM HEIGHT where my fren could turn more smoothly.

So, from what u guys said, when everything (except motors) is mounted on, the leadscrew should turn quick smoothly with hand/fingers.....
Andy

victorbl
01-16-2005, 03:26 AM
Hey Andy, Moondog is probably right. I'm building a machine with a similar setup as yours (ACME lead screw with delrin nut) with the same scenario on my Y axis. Basically, everything would spin freely when not bolted to the carriage, but once secured, it was incredibly hard to turn the ACME lead scew. The problem was the hole through the Delrin was not perfecly perpendicular to the mounting surface of the carriage.

To correct this, I'm planning on threading the Delrin nut with a piece of scrap ACME lead screw, and mount it on a jig that will hold the ACME rod perpendicular to a sanding disc on my table saw. I will then slowly bring the Delrin nut to the sanding disc until it has 'corrected' the misalignment by sanding down the mounting surface of the Delrin perpendicular to the lead screw.

coherent
01-16-2005, 10:32 AM
looks like you got the answers you were looking for. A couple of things to note... Although self tapped delrin, nylon or pvc will work, temp changes may have some effect on the friction depending on how tight things are to start with. You should be able to turn your coupler/acme screw even with the motors attached (no power applied of course). Use a drill motor and run your tap back and forth a number of times to make sure the nut runs nice and smooth and doesn't bind. I initally thought my machine rand pretty smooth with acme screws and a delrin nut setup like mentioned here, but decided to spend a bit more and go with ballscrews. Check the prices at Ronin they really aren't much more than the acme screws and nuts at McMaster Carr. Befire I mounted them, I could hold the ballscrew nut and screw at about 45 degrees and the screw would rotate down the nut freely on it's own. With the acme 3/8-8tpi screws and the acme nylon nuts (from mcmaster carr) I was getting 35-40 ipm rapid moves and at much more than that, the 276oz steppers didn't have enough torque to go faster. I could get about the same or a tiny bit better with home made delrin nuts. I changed to 5/8 5 tpi ballscrews and can now rapid at 180 ipm, so the difference was substantial on my machine. All other things considered (screw type, nut type, tpi, motor size, linear rails/bearings etc), the place on your machine where torque/power is most effected is screw to nut friction!
-marc

andyew
01-16-2005, 11:15 AM
Thanks Victor and Marc...

I think it's really about misalignment and i suppose i'll need quite a few hours to "optimize" the 3 axes to smooth out the delrin+leadscrew system...

As for the ballscrew, it seems very interesting especially at certain diameter, it's quite cheap and will really consider it for my 2nd ver.

Will let u guys know how things going here when i've finished with alignment...Thanks aagain

Andy