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m_c
09-09-2012, 02:01 PM
After much weighing up the pro/cons of going the mill conversion or router from scratch route, I've pretty much decided a well made router is the way to go for now.

I want at least 300mm x 300mm work area, with enough height to add a 4th axis at some point in the future. Main initial use will be plastic, but I want good aluminium capability for some future items, so designed to allow use of coolant i.e. rails/screws well protected from anything on the table.

So, current notepad doodles have come up with the following.

X-axis has about 400mm travel, with 200mm wide gantry sides.
Y-axis has about 350mm travel, with a 150mm wide/200mm high Z-axis mounting plate.
Z-axis has about 200mm travel, with bearing rails on spindle mount plate.

As I'd like to use profile rails, the main construction will be Alu plate and extrusion.
The main table will be U-shaped with open ends. X-axis rails will be mounted on the outside along with the twin ballscrews to give maximum protection. I'll probably go for twin steppers, as it's far simpler from a design/build point especially since I'd like to keep the ends clear.

Height from table to gantry I've currently got as 200mm, but I may drop this to 150mm once I consider 4th axis options.

Current plans are 20mm profile rails for all axis, along with 1605 ballscrews.
I've priced the bits from Zapp to get an idea of costs, but need to explore the other options.

As for the sides, I'm not sure whether to go for 15mm or 20mm thick plate. Price wise there's not too much difference, but will there be much difference in stiffness?


I'll try and get some time this week to get some drawings done in Sketchup.

blackburn mark
09-09-2012, 02:57 PM
As for the sides, I'm not sure whether to go for 15mm or 20mm thick plate. Price wise there's not too much difference, but will there be much difference in stiffness?

the gantry sideds?.... 20mm! even if the flex isnt much better the added weigh will help dampen resonance
im convinced every single bit of weight and stiffness you can get will earn its keep over and over
i guess the weight has to be watched if you want good acceleration but id go for quality of cut over speed if i had a choice

Robin Hewitt
09-09-2012, 11:02 PM
Want to cut aluminium? FWIW could I suggest a different way to make the machine?

Start with a good solid base, a couple of thicknesses of beech worktop sounds good. That's your anti-vibration inertial lump.

Put an aluminium plate, side to side, across the middle. About 8" wide sounds good. It's only a washer so it doesn't have to be too thick.

Bolt the gantry to the plate and base. Butress it. Get a good solid Y axis.

Bolt profile rail blocks facing upwards on the plate to hold 2 rails 8" apart. Screw the rails to the bottom of a 12 x 20 bed plate. You now have a good solid X axis. Your cutter will never be more than 4" from 2 carriage blocks in Y and 4 carriages in X.

Because the X bearings are only 8" apart you can use one screw up the middle, it isn't going to twist. Don't make life difficult trying to drive 2 motors together.

Make the sides of the gantry too tall so you can move the whole Y,Z assembly up when you come to do your 4th axis.
I'm expecting to be told I am out of my tiny mind, let's see what they can come up with :joker:

JAZZCNC
09-09-2012, 11:20 PM
I'm expecting to be told I am out of my tiny mind, let's see what they can come up with :joker:

Your out of your tiny Mind. . :encouragement:

No seriously I see where your coming from robin with this size machine but SORRY can't agree on the choice of material for the base and foundation of the machine.?
A living and breathing material like wood is not a good idea for the foundation of machine IMO.

The rest I can agree with on this size machine.

I'd say make it a fixed gantry if you want it strong and have the space.!

Robin Hewitt
10-09-2012, 12:23 AM
can't agree on the choice of material for the base and foundation of the machine.?
A living and breathing material like wood is not a good idea for the foundation of machine IMO.

But beech is so much more acceptable for her indoors than the bloke alternatives.
It just wants a good solid lump connected intimately to the workings :beer:

m_c
10-09-2012, 01:19 AM
mmm...never thought about going fixed gantry. Biggest issue I can see with that is if I do end up running coolant. I know misting is an option, but flooding is easier to contain.

Adjustable height gantry could be possible, but I'd probably just leave it at whatever height it would need to get a 4th axis, so wouldn't really be any benefit.

Robin Hewitt
10-09-2012, 11:46 AM
It was only a concept suggestion, it's your machine, make it any way you want :rugby:

I don't quite see how a fixed gantry precludes flood coolant though, doesn't it make it easier?

JAZZCNC
10-09-2012, 07:24 PM
mmm...never thought about going fixed gantry. Biggest issue I can see with that is if I do end up running coolant. I know misting is an option, but flooding is easier to contain.

Adjustable height gantry could be possible, but I'd probably just leave it at whatever height it would need to get a 4th axis, so wouldn't really be any benefit.

Nah the fixed bed doesn't make it any harder to have coolant, It's just the same has a milling machine but with the bed moving in only one Axis and the column becoming the 2 fixed gantry sides. Just sit the whole thing in a collection tray or metal enclosure.?

I prefer blown mist cooling for aluminium anyway. Flood is ok if it's proper massive flood but you can't see what's going off where has with mist you see every thing and the cutter is mostly chip free so not re-cutting.
Not saying it's better than Flood just it's my pref unless real big flood so all chips are washed away and this can get very messy so enclosure very much needed.!!

Jonathan
10-09-2012, 08:02 PM
Just sit the whole thing in a collection tray or metal enclosure.?

Maybe m_c doesn't have the space required for the bigger enclosure required to accommodate a moving bed machine? I think the inconvenience of having a large enclosure is negligible compared to the advantages of having a fixed gantry.

JAZZCNC
10-09-2012, 08:30 PM
Maybe m_c doesn't have the space required for the bigger enclosure required to accommodate a moving bed machine? I think the inconvenience of having a large enclosure is negligible compared to the advantages of having a fixed gantry.

Possibly but that still doesn't make having flood cooling harder on a fixed gantry and that was the point.! . . . Plus the tray wouldn't need any more space than the machine requires anyway.!

m_c
10-09-2012, 09:05 PM
My concern with the fixed gantry option was how to protect the x-axis rails from the coolant, but having actually thought about it, it's probably easier.

I just need to make sure they're spaced up of the drain tray, and have a lip hung down around the table so that any run-off can't run along and under the table.
Now would you have the rails or the blocks stationary?
I can think of pros and cons to both methods, but don't think it would make any noticeable difference anyway given the sizes involved.

Robin Hewitt
10-09-2012, 09:44 PM
Now would you have the rails or the blocks stationary?

The X axis rails? You have the blocks stationary under the gantry, anything else defeats the whole purpose. You support the bed where it needs supportingt. Am I not understanding?

JAZZCNC
10-09-2012, 09:54 PM
Now would you have the rails or the blocks stationary?
I can think of pros and cons to both methods, but don't think it would make any noticeable difference anyway given the sizes involved.

I'd have the rails stationary with bearings at the extremes of table but like you say at this size then it's no big deal.

m_c
11-09-2012, 02:35 AM
I've been thinking about it some more, and just skecthed both options.

Fixed bearings
+) Shorter rails. With fixed rails, ideally you need the bearings mounted at the extremes to avoid the working area overhanging the bearings, so you ideally need the rails extending the axis travel past the end of the work area. With fixed bearings, the bearings can be positioned closer together, as the supported area will always remain below the spindle, off course depending on how the table is loaded, it could lead to it bowing.

Fixed rails
+) Lighter table. 4 bearing blocks are far lighter than two rails.



I'm still undecided between fixed v. moving gantry.
I can see the pros and cons of both, but I'm currently swaying towards moving as it means a relatively constant moving weight (moving table means I'd have to tune for it potentially having a lot of weight mounted on it) and it gives me a bit extra flexibility for table loading (could work with longer length materials with less precutting required). Available space isn't a major concern

Robin Hewitt
11-09-2012, 10:47 AM
Fixed rails
(+) Lighter table. 4 bearing blocks are far lighter than two rails.

Surely a lighter table is a minus. Vibration is the enemy and dead weight dampens vibration.

Same goes for the gantry, bolting it to a dead weight reduces the rattle.

Power to move a heavy table/workpiece ceases to be a problem the moment you start using ball screws. You get an enormous push.

Tenson
11-09-2012, 01:54 PM
Has anyone used constrained layers to help dampen vibration and resonance in a machine? I'm thinking for the gantry you could use the normal 16mm slabs of alu but also affix an additional 6mm sheet with green-glue (http://www.greengluecompany.com/). The thinner the layer of green-glue the more friction it generates so the more effective at damping.

Rogue
11-09-2012, 03:13 PM
Greenglue is interesting stuff but have you seen the cost involved?!? You have to buy it by the case for a start.

Tenson
11-09-2012, 04:23 PM
About 100 for a batch. Not too bad compared with the cost of metal for building a machine. My gantry has about 250 of metal in it, not including ballscrews and bits.

Rogue
11-09-2012, 05:01 PM
It's supposed to take 1-2 tubes per drywall sheet so if you're doing up a room then it works out by the case. How much are you planning to use on the machine?

I've not heard of it being used on metal. That's quite an interesting question to ask.

I'm not saying it's a bad idea, I'd just find it hard to justify that outlay for (in effect) a single tube of greenglue. Unless you plan to sell off the other tubes or you have other soundproofing projects lined up, of course. If you're selling off the single tubes you could probably find a few buyers without too much hassle. I'd have a tube off you!

Tenson
11-09-2012, 05:45 PM
Green Glue - Single Tube - Revolutionary Sound Proofing | eBay (http://www.ebay.co.uk/itm/Green-Glue-Single-Tube-Revolutionary-Sound-Proofing-/120720532503?pt=LH_DefaultDomain_3&hash=item1c1b812417#ht_3052wt_1139)

Rogue
11-09-2012, 06:02 PM
:D I stand corrected! So are you going to give it a go?

Tenson
11-09-2012, 08:06 PM
No I just wondered if someone else had tried a similar thing!