Re: Bench-top or welded frame
Again can't be arsed to read all previous posts but I get the gist you want to aluminum but there are other areas of design that could be better worked on than building a base which could hold up blackpool tower without flexing.
Also, do you realize just how much heat will go into those joints so closely connected and how much distortion will occur from that heat.?
The frame needs to be strong but doesn't have to be massively built because the cutting forces are mostly lateral. If Was using cutting 250KG blocks of Aluminium then yes go big to stop defelction but doubt you will be.
The best thing you could do to give best cutting capability in hard materials is to build strong gantry and think about how can keep cutter deflection to a minimum.?
Cutter deflection comes from a mixture of Z-axis/spindle and Gantry vibration/deflection. Gantry deflection is easy dealt with by building strong. Z axis/Spindle is not so easy because this impacts on other areas of machine like travels, tool lengths, clearences etc.
If want high clearance for thicker material or long tools then Long z-axis required which deflects more.
Likewise if only cutting thin material then a lower clearance allowing shorter Z axis is possible, but still got to account for tool lengths, clamps etc.
One option is to lift material to the tool and keep Z extension to a minimum but this isn't practical if wanting to cut range of materials and soon gets pain in arse lifting and surfacing bed each time moved.
But with little out the box thinking, there is a better way which allows Minimum tool deflection of any machine setup while still having high clearance. In fact, can have very high clearence and still only have delection equal to tool stickout.?
This is done by Getting rid of the Z axis altogether and raise/lower the whole Y axis. This way the only deflection is from the tool stickout and any deflection in the gantry beam and supporting frame.
Build the support frame and Gantry beam strong enough and then the only deflection can come from tool it's self regardless of clearence and material thickness.
Because your lifting the Gantry beam which spindle runs along fixed to solid back plate you remove the Z axis from the equation altogether so then can have very high clearence and still have low deflection because there isn't a Z axis to deflect only the length of tool sticking out the spindle.
3 Attachment(s)
Re: Bench-top or welded frame
Quote:
Originally Posted by
JAZZCNC
This is done by Getting rid of the Z axis altogether and raise/lower the whole Y axis. This way the only deflection is from the tool stickout and any deflection in the gantry beam and supporting frame.
Build the support frame and Gantry beam strong enough and then the only deflection can come from tool it's self regardless of clearence and material thickness.
Because your lifting the Gantry beam which spindle runs along fixed to solid back plate you remove the Z axis from the equation altogether so then can have very high clearence and still have low deflection because there isn't a Z axis to deflect only the length of tool sticking out the spindle.
This is going off-thread, but you have got me thinking. Particularly as I've committed to buy a Chinese pack of rails and screws, delivered in the next week or so (as much to get me motivated to get off my arse and do something). I'm not a fan of spending a weekend playing with F360, but, and considering this is a fragment of a design (until I get the bits and validate the generic CAD models I've been using are broadly appropriate), is this the sort of thing that you're talking about, and is this a viable starting point for a design.
Attachment 23827Attachment 23828Attachment 23829
Basic design centred around the 400/700/1000 lengths sold cheaply. Steel box for the end cheeks (okay, only one in the images, but you can imagine the mirrored cheek), as well as the gantry. 100x50x4 mild steel box section. Spindle mount on 15mm aluminium tool plate. Some poetic license at this time with the mounting of the rail direct to the box section - but I don't think I need to model the epoxy at this time. Clearly I'd need to slave the Z-Axis drives and source a second 400mm screw but this isn't the end of the world.
I don't want to waste more time in F360 on this design if it's a non-starter, so would appreciate your view if this addresses some of the rigidity issues.
Re: Bench-top or welded frame
Quote:
Originally Posted by
Doddy
This is going off-thread, but you have got me thinking. Particularly as I've committed to buy a Chinese pack of rails and screws, delivered in the next week or so (as much to get me motivated to get off my arse and do something).
Well I'm surprised at that.? Thought you'd been around long enough to know better than that.! . . . . Design first then buy later is golden rule.
Quote:
Originally Posted by
Doddy
I'm not a fan of spending a weekend playing with F360, but, and considering this is a fragment of a design (until I get the bits and validate the generic CAD models I've been using are broadly appropriate), is this the sort of thing that you're talking about, and is this a viable starting point for a design.
Yes that's the idea thou wouldn't fasten between those two gantry uprights as it will make setting up difficult with little room for error.
Fasten rails on front, ballscrews on side and put brace between gantry uprights at top. Connect two ballscrews with belt and single motor running along top of brace.
Put rails on front of gantry and ballscrew on top.
Re: Bench-top or welded frame
Quote:
Originally Posted by
JAZZCNC
Well I'm surprised at that.? Thought you'd been around long enough to know better than that.! . . . . Design first then buy later is golden rule.
I seriously need to commit or I'll end up chasing squirrels. It's not big, not clever, but it works for me. Also, this is entirely hobby work for me which gives me a slightly different outlook than some others.
Steel is cheap (although my time is precious - to me at least)
Quote:
Originally Posted by
JAZZCNC
Yes that's the idea thou wouldn't fasten between those two gantry uprights as it will make setting up difficult with little room for error.
Fasten rails on front, ballscrews on side and put brace between gantry uprights at top. Connect two ballscrews with belt and single motor running along top of brace.
Put rails on front of gantry and ballscrew on top.
Yeah, was already thinking about the top brace. Wasn't worried about two steppers, slaved, but I suppose rotate the screws 180 and belt across the top - yeah, that'd work and save some complication later on.
Ballscrews on (in)side - I lose a lot of Y travel - struck me during this the depth of the pillar blocks is pretty significant. I'll draw something up and have a ponder. Rails on the front sounds a lot easier.
Cheers - I appreciate the input.
2 Attachment(s)
Re: Bench-top or welded frame
Quote:
Originally Posted by
JAZZCNC
Yes that's the idea thou wouldn't fasten between those two gantry uprights as it will make setting up difficult with little room for error.
Fasten rails on front, ballscrews on side and put brace between gantry uprights at top. Connect two ballscrews with belt and single motor running along top of brace.
Put rails on front of gantry and ballscrew on top.
Dean,
I've been thinking about this a bit, and been through different iterations of a design for the gantry, as always trying to work out the best compromise. Most recently I've been measuring the width of the shed door opening - I don't want a machine that I have to dismantle to get in/out of the shed.
Can I pick your brains on the following - it does, I think, have problems but I simply don't know if they are problems that I need to be worried about.
Attachment 23872
My concern is the projection of the spindle substantially away from the rails.
For info: Y-Axis beam is 80x120x5 box steel. Uprights are 100x100x5. Braces and bottom skids 100x50x4 . Sizes chosen on the "big is good" rule of thumb but also with a mind towards availability and ease of mounting stuff. Shiny stuff is 15mm alu tool plate. There's imaginary bracketry involved tbd. Of course there'd be a brace across the top, made from similar big-steel.
The obvious solution for the projection is to place the spindle assembly on the other side of the Y-gantry (this was my previous design), but I have a real-life constraint (the shed door width, and sensibly the amount of real-estate that this can take up) that means I'd seriously compromise the available space in the Y-plane (this current design obviously impacts the X-axis a bit - but I can tolerate that more than the Y).
Attachment 23877
Kind of shows the impact having the ball screws on the inner face gives me. There's also another issue that the (invisible) top-brace then impacts the available Z-height with the spindle impacting the brace (something I can bodge around somewhat inelegantly by offsetting the brace).
I have looked at replacing the Y-Axis with just a big block of tool plate (20mm), but the deflection calculators suggested a pretty terrible performance by comparison to box section.
My real question is one of opinion - of whether the spindle offset will impact the performance enough to make this design impractical - if you have any thoughts I'd appreciate them.
1 Attachment(s)
Re: Bench-top or welded frame
Quote:
Originally Posted by
Doddy
My real question is one of opinion - of whether the spindle offset will impact the performance enough to make this design impractical - if you have any thoughts I'd appreciate them.
Well think you could afford to go with something like this setup with you having ball screws on inside and not lose to much travel.
On original design with 100mm wide bearing plates and the gantry going to outside edge the spindle centre line will actually be over the linear bearings or very close. So if you used say 80x40 for the diagonal you would still have room for railbearings and only lose probably 40mm or so of travel.
To be honest I don't think the over hang is massive anyway and provided you build it strong then won't have massive affect. End of the day the extension is still less than most Milling machines.
Personally I'd build a wider door in my shed than compromise the machine.
Attachment 23882
Re: Bench-top or welded frame
Much appreciated - I needed a fresh perspective - 40mm loss of travel is affordable (and should save a reasonable chunk on the X axis in the process).
(I'm avoiding going wider on the machine - yes, it's a compromise, but I am somewhat space-limited - too wide a machine is simply impractical for me)
Re: Bench-top or welded frame
Quote:
Originally Posted by
Doddy
Dean,
I've been thinking about this a bit, and been through different iterations of a design for the gantry, as always trying to work out the best compromise. Most recently I've been measuring the width of the shed door opening - I don't want a machine that I have to dismantle to get in/out of the shed.
Can I pick your brains on the following - it does, I think, have problems but I simply don't know if they are problems that I need to be worried about.
Attachment 23872
My concern is the projection of the spindle substantially away from the rails.
For info: Y-Axis beam is 80x120x5 box steel. Uprights are 100x100x5. Braces and bottom skids 100x50x4 . Sizes chosen on the "big is good" rule of thumb but also with a mind towards availability and ease of mounting stuff. Shiny stuff is 15mm alu tool plate. There's imaginary bracketry involved tbd. Of course there'd be a brace across the top, made from similar big-steel.
The obvious solution for the projection is to place the spindle assembly on the other side of the Y-gantry (this was my previous design), but I have a real-life constraint (the shed door width, and sensibly the amount of real-estate that this can take up) that means I'd seriously compromise the available space in the Y-plane (this current design obviously impacts the X-axis a bit - but I can tolerate that more than the Y).
Attachment 23877
Kind of shows the impact having the ball screws on the inner face gives me. There's also another issue that the (invisible) top-brace then impacts the available Z-height with the spindle impacting the brace (something I can bodge around somewhat inelegantly by offsetting the brace).
I have looked at replacing the Y-Axis with just a big block of tool plate (20mm), but the deflection calculators suggested a pretty terrible performance by comparison to box section.
My real question is one of opinion - of whether the spindle offset will impact the performance enough to make this design impractical - if you have any thoughts I'd appreciate them.
Hi doddy,
What work area are you aiming for?
Did you concidder going vertical?
This might solve some of your space problems.
And you could move through doors more easy.
After reading a lot of the comments on peoples 1st designs, i basicly wanted 3 things.
-A simple and heavy bed/frame
- A simple and rigid gantry.
- The spindle within the boundaries of the gantry x axis bearings.
Will there be a rigid fixed connection between your gantry sides?
How do you prevent gantry going out of square?
Your design does not look like it has a rigid gantry now.
Is it made out of 3 separate moving parts?
I think it will be very hard to get a rigid end result that way.
Also the spindle is not in between the linear bearings, this also does not help for rigidity.
Now for me i am no expert.
So please have the more experienced guys here point you in the right direction.
I started my cnc design reading at cncroutersource then came here :-)
Still on a steep learning curve.
My 2cts worth,
Grtz. Bert.
Verstuurd vanaf mijn SM-A320FL met Tapatalk
Re: Bench-top or welded frame
Quote:
Originally Posted by
driftspin
Hi doddy,
What work area are you aiming for?
Bigger than my StarMill (160x100!). Height isn't a massive issue for me (at least not as yet), but 200mm would be an aim. X/Y = around 600x400 was my goal.
Quote:
Originally Posted by
driftspin
Did you concidder going vertical?
This might solve some of your space problems.
And you could move through doors more easy.
Only the crazy people go vertical! Actually, it's something I had just started to think about - I know Dean here has done this in the past. That might be the next machine.
Quote:
Originally Posted by
driftspin
Will there be a rigid fixed connection between your gantry sides?
How do you prevent gantry going out of square?
Your design does not look like it has a rigid gantry now.
(assuming you mean square across the Y-Axis) Yes, a beam across the top, with gusset plates to hold square (sorry, the design is obviously incomplete - more to get the concept right in my mind before burning hours on Fusion 360).
Quote:
Originally Posted by
driftspin
Is it made out of 3 separate moving parts?
I think it will be very hard to get a rigid end result that way.
Yes, more steel to be added yet. As above, this is just a basic geometry sanity check.
Quote:
Originally Posted by
driftspin
Also the spindle is not in between the linear bearings, this also does not help for rigidity.
Now for me i am no expert. So please have the more experienced guys here point you in the right direction.
I started my cnc design reading at cncroutersource then came here :-) Still on a steep learning curve.
My 2cts worth,
Verstuurd vanaf mijn SM-A320FL met Tapatalk
That's exactly why I posted this. Placing the spindle where I did I'm very conscious that it's putting a large force on the rails. Having said that, better and brighter people than me have suggested that the rails are more than strong enough for anything a small machine like this is likely to throw at them, and Dean's earlier comment re. most mills - yeah - they'll place a similar cantilever load on the rails as well.
Re: Bench-top or welded frame
Quote:
Originally Posted by
Doddy
Bigger than my StarMill (160x100!). Height isn't a massive issue for me (at least not as yet), but 200mm would be an aim. X/Y = around 600x400 was my goal.
Only the crazy people go vertical! Actually, it's something I had just started to think about - I know Dean here has done this in the past. That might be the next machine.
(assuming you mean square across the Y-Axis) Yes, a beam across the top, with gusset plates to hold square (sorry, the design is obviously incomplete - more to get the concept right in my mind before burning hours on Fusion 360).
Yes, more steel to be added yet. As above, this is just a basic geometry sanity check.
That's exactly why I posted this. Placing the spindle where I did I'm very conscious that it's putting a large force on the rails. Having said that, better and brighter people than me have suggested that the rails are more than strong enough for anything a small machine like this is likely to throw at them, and Dean's earlier comment re. most mills - yeah - they'll place a similar cantilever load on the rails as well.
Hi doddy,
What is your main problem with exiting 6040 designs?
I feel like the " lean back " gantry design is most space saving.
Do you think 20 mm alu gantry sides will cover your rigidity needs?
http://www.mycncuk.com/showthread.php?t=11610
like that one... but a bit smaller.
Grtz Bert.
Verstuurd vanaf mijn SM-A320FL met Tapatalk
