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

[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

[Jonathan]

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

Surely it all depends on what size cutter / feedrate I'm using - if the cutting forces are not to high etc. I was thinking more using the T slots for clamping wood, and using them to clamp my large milling vice (6" jaw, opens up to about the same) to the table for when I want to machine metals. That's still limiting me to only relatively small bits of metal though. If I want to machine a big sheet of aluminium then it's not going to be more than 8mm thick (cost again), so a 6mm cutter would suffice. What's the cutting force on a 6mm end-mill on aluminium at a decent feedrate? Surely not so much that lots of clamps on MDF won't hold it?

I agree putting steel strips on the bed is a good plan, but again very expensive - unless you know of a better supplier than me! I could skim the existing 18mm MDF bed with the router before putting the steel on top. That should get it reasonably parallel. I guess I could afford to make a smallish steel bed.

(Sorry I probably could have made this post a bit less rambling, I'm just thinking aloud.)

[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

[Jonathan]

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

That's why I suggested in my last post putting a thin sheet of steel under the top MDF layer, so that T-nut is pressing on the steel, not MDF.

I like the idea of threaded inserts, but they're not so versatile as T-slots.