Jill of all trades, but mistress of few !

[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

[Robin Hewitt]

Hi Julie

The cheapest way to rigid is steel box section, but after making the frame you want to make your fittings adjustable because it won't be quite as straight as you require.

If you want long lengths of aluminium bar or box section, I suggest you stray outside the hobby market and go directly to a stock holder such as http://www.parkersteel.co.uk

Robin

[HiltonSteve]

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?

I have not had any experience with many aluminium extrusion suppliers, I used Hepco for my 80x40 and when I ordered it I told them that the 3 lengths needed to be within 0.5mm and cut 90 degrees, when they arrived they were spot on, just tapped the holes and bolted them in.

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-.

You are correct, I used 1 20mm rail each side for the X axis. For the Y axis I used a rail top and bottom of the gantry crossmember which is why I made the crossmember out of 20mm (same size as the rail), made it easier to mount and align. The Z axis has 2 rails running down the front face. So each axis has 2 rails and 4 bearings which make it very solid, no play anywhere at all.

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 used 20mm plate for the gantry sides and the crossmember, the rest is 15mm. I went for these sizes as that is what suited it best when doing the design, bolting 20mm rail to the edge of 20mm thick plate is quite easy! Then thought if the crossmember is 20mm then the side plates need to be so it looks right, then used 15mm for the rest because....well, I did!

Yes it may be over the top and I may have got away with 10 and 15mm plate but it would have made my design more difficult to put together. The cost difference of using thicker material outweighed any potential build problems I may have encountered and also guaranteed a good solid machine. Also I thought about how I could manufacture the parts and what machinery I had available to use, John S did the side plate profiling for me on his beaver CNC then I machined all the rectangular plates one Saturday morning on my mate's bridgeport, then drilled and tapped everything in the afternoon at home, so most of the main structure was made in a day!

The way I did it made sense to me because it was quick and easy to build because of what machinery I had available to make the parts, not everyone has these resources available so you have to do things differently. If I had a CNC mill to play with for a day to make my bits then I would have done things a lot differently!