Jill of all trades, but mistress of few !

[Gary]

I think she means the Y axis.
Moving a large gantry is better to drive from both sides or you can get crabbing even with good quality profile rails.
This is more promenent if you are cutting on one side.

Hi Julie

That's to be avoided like the plague :nope:

First you have to decide what kind of accuracy you want to achieve for the cut. Think resolution. The motor moves the table by one increment. A small increment improves the accuracy of the cut. A large increment improves your top speed which is handy when you want to move 8' ASAP.

When you have an accuracy figure in mind you can decide how to drive it. Screws, rack and pinion, belting? The lower the accuracy the cheaper it becomes. It's all trade offs, what are you trying to achieve? Are we talking mass production where speed is king? Are we talking bespoke and it doesn't really matter if it takes 2 minutes to move end to end at a lowly 2 cm/second?

Robin

[Philmollatt]

Hi all
Just an idea regarding the x axis 2 motor thing, if i were doing it i would put a lead screw/ballscrew on each side conected by a timing belt and pulleys, with a double pulley on one side then drive the second pulley from the motor, also this gives you some flexibility with pulley sizes, small motor pulley for accuraccy large motor pulley for speed. Shoud also work with rack and pinion systems with a long drive shaft.
Thats the way i would go if i were building it from scratch, that way its just the one motor driving both sides of the axis, and a swap out pulley set up with the progam,
Thanks for listening
Still a newbie so dont take me too seriously..

[Smiler]

Hi Julie,

RE: driving the long axis with 2 motors. You don't have to with R&P!

All I did was to make a shaft with a pinion on both ends and a drive pulley inboard of one of them. Then simply mount the motor in line with the pulley and you are driving both sides of the gantry with 1 motor, no crabbing, simples.

If you want to get fancy you can use a zero backlash pinion on one end but I didn't think it needed on a router.

Jeff.

[Gary]

The principle is the same if using screw or rack.
drive it from both sides and you won’t have a problem.

[Smiler]

The principle is the same if using screw or rack.
drive it from both sides and you won’t have a problem.

Of course it is. However, once you get into long travel lengths, unless you need the super duper accuracy of ballscrew then IMO R&P wins hands down. It is also much easier/mechanically simpler to drive both sides of a rack with a single motor and a single motor is what I would propose. Maybe Techserve could give us some insight on how they do things on long axes.

End of the day this is a router and R&P will give Julie all the accuracy she needs whether she is carving long panels or cutting parts for furniture. All I would suggest is she drives both sides with a SINGLE motor (bought from Zzap).

Jeff.

[Gary]

Totally agree R&P is far better for long axis, and cheaper.
Techserve use R&P, infact most plasma machine manufactures do.
The accuracy that is needed with a router, will be fine with R&P, however, normally will requre some gearing, but simple belt and pulley will do.

Of course it is. However, once you get into long travel lengths, unless you need the super duper accuracy of ballscrew then IMO R&P wins hands down. It is also much easier/mechanically simpler to drive both sides of a rack with a single motor and a single motor is what I would propose. Maybe Techserve could give us some insight on how they do things on long axes.

End of the day this is a router and R&P will give Julie all the accuracy she needs whether she is carving long panels or cutting parts for furniture. All I would suggest is she drives both sides with a SINGLE motor (bought from Zzap).

Jeff.

[Julie]

Hi,

Thanks for all the replies so far. I haven't disappeared as fast as I came, just been doing a lot of reading and research.

This immediateley throws up a load more questions. I hope others will excuse a few really basic ones. For starters:

1. I originally suggested wood / MDF construction, but having seen the construction methods others have used and investigated various suppliers of extruded aluminium profiles, that seems a much better way to go. I have so far come across a number of such suppliers, having downloaded the Valuframe catalogue and checked out the Rhonmac (same system as Valuframe?) and Marchant Dice websites. I've also seen references to Bosch. Is there anything significant to choose between these, or other, systems / suppliers?

2. I've read through all the posts concerning HiltonSteve's very impressive build. If I've understood it correctly, Steve, you've used just one guide rail each side on the x-axis (but 2 for y- and z-axes). Your gantry appears to have additional rigidity through the Al plate that connects each side beneath the bed. At the sort of size table I'm considering (around 8' x 4') I'm expecting to need to use at least 3 legs per side (I envisage it being free-standing, not bench mounted) and, very possibly, at least one under the centre. These additional (non-corner) legs would preclude an under-bed connection between the gantry sides. I'm presuming I would need 2 guide rails per side for the x-axis and 2 for each of y- and z-.

3. Again with reference to Steve's build, the entire gantry / y-axis structure seems very solid with 15 / 20 mm Al plate throughout. Does it really need this for sufficient rigidity? I imagine I will have a greater need for care here with a 4ft + y-axis, but was hoping that the use of extruded profile with, perhaps, rather thinner Al sheet skinning would suffice. Am I kidding myself?

I will shortly be exiled from the internet for a couple of weeks, so won't be replying again for a while, but this will give me some quiet time for further planning.

Julie