1.7*0.74*0.4m Mill / Router building...

[Jonathan]

im still pondering the options for my fourth axis, im leaning towards a 50:1 harmonic with a stepper... it'll only be on light duties

Could you use a timing belt inside the harmonic gearbox as the flexible gear thingy? Milling the inside out pulley would be fun. Probably do it in two semicircles...

youve got me thinking now though.... it would be nice to be able to isolate the gearbox and run it up to lathe speeds

Yep, that's my plan ultimately - to be able to accurately switch between stepper and brushless motor drive.

Made good progress on the router today. Milled and drilled aluminium box section and channel to mount X axis linear bearings. Also drilled and milled one side of gantry to fit that, and put slot in for timing belt to go through. Lots of smoke and blue swarf when drilling the steel. It's a 20mm wide slot so I chain drilled @ 16mm (biggest I have) to save time with the 20mm milling cutter. Will probably make more sense when I put photos tomorrow.



I'm 14 holes and one slot away from finishing :) Plus a bit of assembly and wiring I suppose.

[blackburn mark]

Could you use a timing belt inside the harmonic gearbox as the flexible gear thingy? Milling the inside out pulley would be fun. Probably do it in two semicircles...

haaha!!!! you read my mind this time :) iv already considered it, not really explored it deeply though, you would need a clever way to output the torque from your inside-out timing belt to your output shaft
the beautful thing about using a belt for the strain wave gear is its so flexble you could use two simple bearings or rollers for your wave generator and use a slightly larger timing belt for the outer gear and pre-load it with your simple two bearing wave generator....
im thinking it would take quite a bit of elegance to make it work... backlash might well be very small but with heavy cuts im thinking it will have quite a bit of give
errrrr..... i dunno ??? youve got me thinking on the issue again.... if i try to fit any more in my head i think one of my eyes might pop out :)

Edit: not sure why you would need to cut the internal in two halfs ?? i dont think you would need sharp corners at the root end of the pitch

[Jonathan]

...use a slightly larger timing belt for the outer gear and pre-load it with your simple two bearing wave generator...

Surely a timing belt for the outer gear would have the wrong profile.

Edit: not sure why you would need to cut the internal in two halfs ?? i dont think you would need sharp corners at the root end of the pitch

Maybe we are talking on cross purposes. I suppose it depends on the timing belt you choose. If it's one with round teeth then you could CNC mill it easily without a 4th axis. If it's say XL then you'll want to mill it with a 4th axis, but clearly the chuck will collide with the other side of the pulley when it's milling the teeth, unless you did it in two halves...or more realistically thirds.


Finished all machining for router this morning! *Just* needs assembling - waiting on my dad to put some bigger legs under it since the previous arrangement was designed for a 10kg gantry, not >50kg!

Been thinking about how I can clamp stuff to the bed to machine it. It would be nice to have T slots like on my milling machine since then I could use the same clamps and easily put the vice/rotary table etc on it. I do have some HSS T slot cutters however I think cutting MDF will destroy them.
My plan is to buy two sheets of 18mm MDF. Glue/screw one down to the bed, get the router to cut the wider part of the T in that and level it, then put another sheet of MDF on top of that and cut the top of the T slot. That way I can use standard router bits...My only worry is if MDF is going to be strong enough?

Just been making collets for the cheap router I'm using. I'll post a video here soon...

[Wobblybootie]

giving the MDF a few coats of thin epoxy should provide some strength ... thin enough to soak in at first but not too much otherwise the MDF will swell an alternative could be the single T slot strips from Axminster or Rutlands etc. secure them to the lower panel and infill the spaces with the upper panel ...

[M250cnc]

Been thinking about how I can clamp stuff to the bed to machine it. It would be nice to have T slots like on my milling machine since then I could use the same clamps and easily put the vice/rotary table etc on it. I do have some HSS T slot cutters however I think cutting MDF will destroy them.
My plan is to buy two sheets of 18mm MDF. Glue/screw one down to the bed, get the router to cut the wider part of the T in that and level it, then put another sheet of MDF on top of that and cut the top of the T slot. That way I can use standard router bits...My only worry is if MDF is going to be strong enough?

Sorry but you are gonna be wasting your time using MDF and an accident in the making for sure.

giving the MDF a few coats of thin epoxy should provide some strength ... thin enough to soak in at first but not too much otherwise the MDF will swell an alternative could be the single T slot strips from Axminster or Rutlands etc. secure them to the lower panel and infill the spaces with the upper panel ...

More bad advice The only thing MDF should be used for is a spoil board

Phil

[Jonathan]

Sorry but you are gonna be wasting your time using MDF and an accident in the making for sure.

Can you think of anything better to use that's not too expensive? Maybe plywood, but I guess that's not much better. Vacuum table isn't much good for metals. Bear in mind it needs to be about 800x1900mm ... so clearly I can't afford a nice piece of tooling plate that size!

I'm not sure about the epoxy idea either, wouldn't it just crack/crush?

Making collets for router:

http://www.youtube.com/watch?v=m98fPg-_vUU


Not quite sure with what you mean by exiting the belt through the outer wall, diagram?
I agree buying one is probably the safest option! If you're after a really big reduction then perhaps several timing belts and pulleys could work. If each one gives 1:4 (feasible I think) then you only need 2 belts to get close to 50:1. Timing belts don't have backlash, but I'm not sure about stretching. Why do you want such a high ratio anyway? My rotary table is 1:90 and it takes forever to rotate, even with the 70v stepper drivers.

[M250cnc]

Can you think of anything better to use that's not too expensive? Maybe plywood, but I guess that's not much better. Vacuum table isn't much good for metals. Bear in mind it needs to be about 800x1900mm ... so clearly I can't afford a nice piece of tooling plate that size!

I'm not sure about the epoxy idea either, wouldn't it just crack/crush?

Jonathan any type of wood table is going to fail to sufficiently clamp metal to it

Whatever you are machining/clamping to the table has to be weaker than or equal strength to the table itself. So the minimum would be ali but it would be cheaper to use steel.

A steel plate with 50x15 bars with 70x15 bars mounted on top to form the tee slots your require, and steel would be my preferred material.

Steel wont warp when wet/different humidity you would have to set your X & Y Axis to run parallel to the plate, now you might think this is a disadvantage not being able to machine the bed to suit the X & Y

But you can only get a flat surface this way if the material is thin as a very thick piece will show any misalignment.

Phil

[blackburn mark]

Whatever you are machining/clamping to the table has to be weaker than or equal strength to the table itself

iv heard this said a few times... im not sure i agree with that phil, surley the table only has to "equal and opposit" the cutting force and carry the weight of the job.... you could use blu-tac as long as it did just this :)

[Wobblybootie]

Sorry, I had not read the whole thread, I assumed that with a bed of the size you have, you would be machining wood etc. Phil, there are plenty of machines out there using an MDF surface, the MechMate springs to mind and that is one serious machine!! Others use the threaded inserts in the lower board and epoxy to secure them with a drilled replaceable spoil board above. However I guess to machine metals you will be using some form of coolant in which case MDF is a total NO NO.

[M250cnc]

The point is, this type of clamping just will not work for a machine vice 4th Axis etc.

The Tee Slot nut will just pull straight out through the MDF or you only clamp with finger pressure:rofl:

Phil