Is anyone able to give me a rough order of magnitude for the sort of price I will be paying for having the custom aluminium parts (gantry side etc) machined? I really don't have too much of an idea right now!
Cheers,
Dave
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Is anyone able to give me a rough order of magnitude for the sort of price I will be paying for having the custom aluminium parts (gantry side etc) machined? I really don't have too much of an idea right now!
Cheers,
Dave
Just my 2p worth... I'd say you have a lot of designing still to do. My guess is that you will replace some of that extrusion with plate and you'll probably add more (machined) plate into the design. Any guess at a machining cost at this stage would be unrealistic I think. You might also like to consider whether your design will require machining on both sides of any plate as that will increase the cost due to the set up time needed to machine one side, flip the plate and align it accurately for machining on the other side. If you have a look at my design I've specifically made it so that it can all be machined from one side with the exception of some counterbores that I'll do myself. Lets put it this way, I spent a lot more on parts than I did / will on machining costs.
Thanks for the help, I will try and keep all parts machined one side only.
Slowly but surely I'm starting to make some progress...
Attachment 12714
My thread moved?!
Small update...
Attachment 12733
Now I've mounted the FF blocks on the outside of the plates I don't think I'll get an off-the-shelf motor mount which will fit over them? So I might need to use pulleys?
Pulleys are the way forward, they give you flexibility in the final machine and generally make the design simpler. It's slightly more expensive to use pulleys rather than a direct connection and there are more moving parts which means more points of failure but I think that's a small price to pay.
One thing I would say about your design is start pricing it up. I'm guessing those corner connection blocks are the 90x90 ones - they are quite expensive if you need a load of them and they don't result in a machine that is all that stiff (they are great for display stands, not so great for machines). Once you start getting into the nitty gritty of placing components and pricing up I think you'll begin to consider using aluminium plate and box section more.
Looking good though.
You are very right. I have been keeping an eye on the cost and realising that it soon adds up. The reasons why I am not leaning towards a steel box section frame; the first is I don't have a MIG welder! The second is that even if I could justify purchasing one then I cannot see how people manage to weld everything so that it is all square and flat? In my mind that would be quite a hard thing to achieve?
I was meaning aluminium box section, you can get some really large sizes if you shop around. It's more expensive than a frame made from steel box sections but it's easy to work with and the supplier will cut it to length normally (I used aluminium warehouse iirc).
My first CNC design included a steel frame and I actually rushed out and bought a halfway decent MIG welder. I never actually built the frame in the end though, doh! Anyway, you don't need a fancy MIG to weld the steel frame together - a cheap and nasty stick welder from ebay will do the job, there's one up for £26 at the moment. The trouble with MIG is unless you go for one with some grunt it won't handle the 4mm thick box you'd want to build the frame from. As for keeping it square and level if you look around you'd be amazed what can be done with epoxy resin. Basically you weld up the frame as square as you can (lots of small welds + clamps) and then pour very thin epoxy over where you'll mount the x-axis rails. The epoxy will self level and should leave you with two sides that are in exactly the same plane. Check out this thread as Neil will be doing another epoxy pour any time soon (actually the technique in the first pour was fine he just fluffed the mixture).
Dave don't be fooled into thinking profile is flat or level because it often isn't and to make this worse your design makes it so your pretty much guaranteed you'll have issues with the rails binding.? . . .Your relying completely on the quality of cut on those uprights to keep the rails aligned and 90deg to the base. The 90Deg brackets are not accurate enough or strong enough to hold everything square. The fact your using 45x90 orientated in it's narrow section when the Y axis forces will be trying to rock the profile doesn't help and this is compounded by the fact the 90deg brackets don't hold it in that direction either.
Sorry to say this but while you think the frame is strong it's actually weaker than you think because it's not braced or held the directions that matter and your under sizing the profile. To make profile work for this design you'll need 90x90 for all the base and much more bracing in correct locations using plates not those poxy 90deg brackets.
For this reason Steel is much cheaper, stronger and more accurate if used with the epoxy method.
Hmm maybe it's time for yet another re-think then...
I don't want to go OTT with the design but obviously it needs to be useful. What are you opinions on the gantry design as it stands so far? Are there any other alternatives to a steel box section base?
Thanks for all the help,
Dave
Dave don't get me wrong I'm not saying profile won't work because it works great and I use it all the time but it does need to be supported and braced correctly and by this I mean not using in the normal manner profile is used IE: using corner brackets etc. I'm also not saying your design is flimsy or weak just not has strong as you may be thinking. It will certainly have some chatter in harder materials as the frame vibrates.Quote:
Originally Posted by biketrialsdave
For this high side design to work best with profile, esp when on it's thin edge you need to brace the hell out of it using plates.
Your gantry is ok-ish but I would have a bit more strength in the bottom profile as this takes the most the cutting forces. To be honest I'd have the L shape layout of the profile at the bottom but with lower profile laid flat.
I understand your reluctance to weld but it really isn't difficult or needs to be expensive. Don't need a Mig and like as been said cheap stick will work fine.
If you don't want to weld then how about finding someone who can weld and have them do it for you.? If you cut and preped all the steel it wouldn't take someone long to weld that simple frame.! . . 2 hours Max and I'm allowing for a very very slow welder there.!! If all steel was cut and preped it would literially take me 30-40mins tops just for the welding.
Hmm well I do have an arc welder somewhere in the shed. Not touched it for years and was never any good at it! May need to get practicing...
Get it out and get practicing. Don't use old rods and buy good quality rods not some cheap rubbish from car boot as they make all the difference. Keep them dry and stick in oven on low heat for 15 minutes before starting. Welding new metal like Box section is a piece of piss with a stick welder. Also Just realise you don't need Xray quality welds and Just like Snow makes every body's gardens look the same so does a good grinder and paint on pigeon shit welds. . .:encouragement:Quote:
Originally Posted by biketrialsdave
Just pulled it out the garage, its the one in the link below. Very cheap and cheerful. Only a 100A output.. What sort of thickness steel box section would be best to use? 3/4mm?
http://www.metals4u.co.uk/welding/we...sp?prd_id=3124
4mm will be better than 3mm but either will work. With 100A you'll be limited to 2.5mm rods which will be better suited to 3mm.Quote:
Originally Posted by biketrialsdave
I will find all my gear and get hold of some scrap metal sometime this week! :) It's always good when you find a reason to use an untouched tool! Out of interest, how are people bolting their linear rails to box section? Bolt all the way through both sides?
You can't bolt all the way through as it would squash the box section without spacer tubes I used 5mm box section so just drilled and tapped it but others have glued a steel plate inside the box section with gorilla glue and then drilled and tapped. As Dean says you don't have to be super accurate because you can use epoxy on the top with a moat between the rails so that it levels out on the same plane.Quote:
Originally Posted by biketrialsdave
When and if you come to this step just ask as quite a few people on here have used it. I used the Wests System which is ultra slow curing ie 15 -20 hours and so levels out very well ..Clive
Why is it not possible just to drill a bigger hole in the bottom face of the tube and nut up to the underside of the top face? G.
It is possible Geoffrey but to be honest it's not needed. Mostly I use 4 or 5mm without any problems but in the past I've fitted rails to 3mm box with no issues. The fine pitch gives enough threads engaged and because of the number of bolts you don't need to swing on them to tighten down.Quote:
Originally Posted by GEOFFREY
I just use spring washers with loctite on threads and never have any trouble. The rails on my machine are into 3mm box and have been on for over 6yrs without any bolts coming loose so it works well enough.
When I started building my first frame I (stupidly) decided to bolt it together, I was worried but stripping threads etc so I did some experimenting...
The test piece was 4mm steel box section drilled and tapped for use with regular M6 socket screws. With a screwdriver and a hex head I couldn't do the bolts up tight enough to strip or damage the thread in the box section. With a regular Allen key I generally couldn't damage the thread, after repeated re-tightening as tight as I could do by hand I did manage to make a couple of the test holes a bit loose. With a cheater bar on the Allen key I could strip the threads and using a drill driver without torque limiting I could strip the threads. My conclusion was 4mm box + M6 was more than strong enough for what I was doing.
I also experimented with some 3mm box + M6 and concluded it wasn't good enough. You can get a thread in it but it's clearly not much good. M5 worked and M4 (which is what I suspect your rails will be using) was fine.
Yet again, thank you for all the help! I think I may end up going for something like 60 x 40 x 3mm box section as this is within the capabilities of my welder and isn't too expensive.
If you can go with 4mm all the better for drilling a tapping. ..CliveQuote:
Originally Posted by biketrialsdave
Hmm if I can get away with 100A/2.5mm electrodes then maybe. Although it is an added cost...
The rail I have takes M4 bolts so thats 4.28 threads for 3mm and 5.71 for 4mm... I think the rule is 1x the diameter?
Started work on the base...
Attachment 12740
Listen trust me it will be fine. One more added point My machine was mounted vertical for well over a year and other than hanging from the ceiling you couldn't put more stress on the bolts has they had all the weight of the gantry bearing down on them and they didn't even flinch. Go for it won't be problem.!Quote:
Originally Posted by biketrialsdave
Better just put some triangle plates on the front uprights and your sorted.Quote:
Originally Posted by biketrialsdave
Still need to sort that gantry thou and put the bottom profile flat with vertical one above it.! . . . Hard to see from drawing but what size profile is it.?
3mm it is!
Yes, still a bit of work to do on the gantry (motor mounting etc). The profile is 80x40. If I can mount the motor on the outside of the gantry end plates then I was going to put another piece of horizontal profile in to enclose the back completely.
While I'm here, what brands of welding rods do you guys recommend? There's plenty of "Super 6" ones on Ebay (6013) for a good price?
Attachment 12741
Dave,
See screen shot, i had 5 mins spare. The red and green sections would fix to your side plates and then to each other, the profile is 80x80, the plate is 20mm, note the datum for the rails on the front plate.
.Me
How did you manage to edit that, Lee? Thank you! My only concern with that design is that I thought the rails were better off not being on there side?
Hi mate, I pulled your image into the software I use for Web Dev then did some cut and paste magic with what was already there :).Quote:
Originally Posted by biketrialsdave
For these rails it's not as important, open round type bearings, then yes that would be correct. You could still mount them at the top and bottom, the choice is yours really but the objective is to get and keep the bearing units as close to the cutter as you can, that being said the the difference here would probably be negligible. I did a few version's of the mock up and one had the rails as suggested, if you prefer that design add plates to the top and bottom, as well as the back, I forgot to say that the back plate didn't need to be 20 mil though, also going with the top/bottom arrangement also means that the spindle plate/assembly stands further away from the bearings due to the lead screw interference with the ali profile.
Dave slapped this together for you quickly so you can see approximately what you may end up with, without needing to get down and dirty in CAD.
Nothing is to scale obviously as it is just a drawing, note the X Axis screw mount position and that it would probably need moving back (away from spindle) to allow for clearance of the nut and mount (at the spindle plate), side plates would need to be bigger and other plates also bigger, bigger side plates are not a bad thing outside of additional cost because you really don’t want to go any less then 2-250mm centres for your rail bearings, both designs pretty much force you in that direction anyway so I didn’t mention it before but I thought that was a little bit ignorant of me, so here it is.
You could close things up with datum’s and pockets for the rails and bearings and so on, keep an eye on the proportions as well, if you look at the original image I’m working from, the gantry looks small next to the spindle, if something looks small, it probably is...resize to match the proportions if you can.
Also, others will probably say it’s not as important as getting other things right, and they are right but try and keep everything lined up and parallel, so your rails, lead screw and nuts. On the Y Axis (bed) the nut could be moved back towards the spindle in my previous image, vertically aligning it with the rails and lead screw, the middle of that plate “looks” nice but would it be better for the loads, if they are all inline?, they all come together to work as one.
Just my thoughts...What do I know...hope it helps!
.Me
No need for that box design around gantry it add's very little but expense and more potential for binding. Also with this design the ballnut won't fit between the Z axis backplate and gantry. Those wide top n bottom plates with rails sat back just make long levers acting upon the bearings which will could cause binding.!! . . . . Not a design I'd go for.!
Your design in post #67 will be ok. Don't waste money or time on the box around gantry setup no point or bennifit IMO unless bracing sides.!
The significant advantage from putting the rails one the top and front of the top and bottom beams respectively (as Jazz suggested earlier), is that you can make the rails a bit longer and thus increase the spacing of the bearing blocks a bit without widening the machine or loosing travel. I'd certainly recommend that since the stiffness due to the bearings is proportional to the bearing spacing squared (assuming what they're mounted to is rigid etc), so every little helps.
Not much progress but changed the "L" shape on the gantry as JAZZ suggested. I'm now using 2 pieces of 80x120 and 2 pieces of 40x40 (mainly for filling the gap). This used to be 60x30 but thought I better bulk it up. Also the height (total height 350mm) and width (now 175mm) of the gantry side plates has increased a little to accommodate. Still undecided with what to do at the back of the gantry... I need to leave enough room to mount the motor on the inside (using pulleys).
Attachment 12764
Ahhhh! really not sure which direction to go with the gantry design. It just does't look right now. Maybe I should mount the motor on the outside of the plate and the fixed (FK12) ballscrew mount on the inside of the gantry plate? (I.e. direct connection, no pulley).
Who knew this would be so hard!
Lol, I know exactly what you mean. I must have gone through a dozen different designs before I settled on what I was going to build. The most disheartening bit is when you think you've got it done then notice there's a collision or something doesn't quite line up correctly.
I'd be interested to see a front view as your design you seems to have a full height side plate on the gantry. Do your x-axis screws stick out a long way?
"I'd be interested to see a front view as your design you seems to have a full height side plate on the gantry. Do your x-axis screws stick out a long way?"
Not quite sure what you mean by that?
Here are some options for the gantry..really don't know which route to go down now...Option A would allow an internally mounted motor (without increasing the side plate width). However I am also leaning towards option B. No matter which option I go with I still need to do something about the big gap where swarf could get to the ballscrew.
Attachment 12769
Option A isn't going to be very strong, it has almost no vertical bracing. Essentially all the stiffness would come from the bolts through the side plates into the profile.
Option B is ok but Option C is going to be a bit stronger. If you want the space internally to mount the stepper then you could go with option A but put a 10 or 15mm plate across the back (I assume the sloped side is the front). You should really have a look through some of Jazz's threads if you want to see a good design that keeps everything internal, the design I'm thinking of has a 20mm plate a the front of the gantry with a slot machined out of it for the screw connection. It served as inspiration for my design.
If you want to do a quick experiment get a couple of lengths of 2x4 timber and nail them to some ply in roughly the design of option A, it'll take 5 minutes to build and you'll immediately see why it won't work as a gantry as it'll wobble around like a jelly. Grab yourself a bit of hardboard and nail it across the back, you could probably stand on it them.
If you want a simple design that works is strong and neat then try this setup. This machine design with higher sides is just for cutting woods and soft materials but you can use the same "L" arrangement without the high sides. Before anyone says it the ballscrew at the rear makes no noticable difference to cutting and the advantages of keeping chips away from screw are clear to see has is the neatness.
If you want stronger than this then look at the All aluminium gantry but it's much more expensive, thou it is very strong and again neat with good protection to components.
Thanks Jazz! I had thought of something similar but was afraid monting the ballscrew like that would cause problems. Is the general idea of the gantry sides to keep them as short as possible? Well not the sides, but the distance between the top and bottom profile carriages on the X axis?