Marchant Dice router no thrust bearings?

[gavztheouch]

I have been aware of the fact that there are no thrust bearings or any sort of proper ballscrew mounts on my marchant dice router. Up until now it ain't been much of an issue as I was cutting soft mdf and plastic at slow speed. Last week I had a job to cut some birch and I noticed the accuracy to a hit. All my dimensions were consitently off by 0.4mm or so, regardless of the length of the dimension, this sound like backlash. The couplers are tight so I reckon it is due to the fact that the ballscrew does not have a thrust bearing and the design realise completly on the stepper motor resisting the force on the ballscrew. The stepper won't do this as I was expecting, so I think I will prob need some proper mounts.

Has anyone else got a marchant dice A4 sized router with the same prob?

Here is a pic of the current setup. x,y and z are all indentical.

The x axis ballscrew end arrived bent and the coupler had a lot of runout in the machining, so much so that it wiggles the stepper motor a lot as the axis is moved.

[Web Goblin]

I had a bad experience trying to deal with Marchant Dice so I dont go near them anymore. Thats really poor build quality not having any support bearings in place. If the shaft is bent and directly affecting the stepper then it will eventually knacker up the stepper motor as well. If you grab the ballscrew by hand can you get any play in it by trying to move towards and away from the stepper?

[gavztheouch]

Hi Web Goblin,

If you grab the ballscrew by hand can you get any play in it by trying to move towards and away from the stepper?

Yes lots, prob over a mm. :(

If the shaft is bent and directly affecting the stepper then it will eventually knacker up the stepper motor as well.

I know its only a matter of time before it knackers the motor. I actually completely rebuilt the machine last week, had the ball screw in the lathe to check the runout on the ends, straighten it out as best I could. A new coupler would help matters as most of the runout is in the coupler. Actually I thought to myself Ill get some oldham couplers, then I relised I couldn't because the coupler needs to be ridged to work as the motor is holding the screw in place, pretty crap huh.

I know merchant sell multiple routers like this a week I find it stange that they don't support their ballscrews. If they did I think they would have quite a nice product

[Web Goblin]

Your right, an Oldham coupling definetly wont work. Most couplings will be able to take out some axial play but not any along tha axis. You could disconnect the stepper and see if there is any play in the shaft to see how its holding up. Looking at the photo its hard to see what you will be able to modify to add a bearing block to support the shaft. what you might have to do is make a bearing block to fit on the motor side of the vertical support and then an extension shaft to be able to refit the motor and coupling. Saying that you could save a bit of space by making the through hole for the ballscrew larger and recess the bearing block in it.

[gavztheouch]

If I could fit a block in the inside like this I could retain the same mounting block for the motor. I would be a little hesitant about milling into the aluminium extrusion as I don't have a mill.

[Web Goblin]

Yes that should do the trick. Didnt know if you could get it on the inside but if you have enough space that would do. Cant you mill it on your machine?

[AdCNC]

Its shocking to see that companies selling crap like this can get away with it, i my opinion thats not even fit for its purpose. Shocking....

[i2i]

is there anything on the other end of the ballscrew

[gavztheouch]

The other end is floating inside a bearing which is pressed into the gantry extrusion. I thought about welding a new end onto the side that is not driven, then maching this side to take the bearing block. That way the thrust bearing will be on the "wrong" side of the screw but it would mean less mods to the router as it stands. What do you think?

[i2i]

a cost effective route to thrust bearings is to use a deep groove roller bearing on the opposite end of the ballscrew to the motor, which is fixed on the ballscrew and anchored to the frame. This is quite common on lower end machines and often gets mistaken for just an end support bearing. It's not ideal but gives a reasonable amount of thrust protection.