my first build

[irving2008]

Adrian,

A comprehensive and thoughtful post. I have added my thoughts inline below...

Best of luck!

Irving...

... milling alloy would be nice but not a requirement. a realistic decision!

the design will be a moving gantry with a workable area of roughly 2' by 4'. that is not set in stone and may be changed later as i work out the details.

the bulk of my budget will go on a controller/stepper package. i do have some electronics training but i wouldnt be confident in the reliability of anything i could build. since this is an important part of the machine i guess i should get this part right. i dont want to spend hours trying to get the machine working only to find the controller isnt working right. i am looking at a kit from http://www.diycnc.co.uk/html/cnc_systems.html
it is the three axis kit for £207 i am looking at.
if anyone has any feedback on these products, good or bad, i would be interested in hearing it.
The DIYCNC package is used by several of our members and is well thought of, as is its proprietor. For your needs, if budget is an issue, you might consider his earlier System3 single board unit at £97. Dont forget you will need to add a power supply if you dont have something suitable to hand. Look for 30v at 8 - 12A, these can be picked up on eBay relatively cheaply (like this one, get in quick) or DIYCNC do a 24v one at £50.

the machine will be primarily constructed from mdf. i do have a table saw, router table, pillar drill and some other stuff so i shouldnt have much trouble making the chassis. i will keep an eye out for some second hand linear bearings and lead screws but for the moment the good stuff is out of my league so i will attempt to make my own. i will design the chassis with a view to maybe upgrade it if i get the chance. With the savings on the controller you might consider Igus' Dryline-W bearings. I've not used these but the rail is £52/m and the bearing blocks under £7 so pretty price competitive to ball linear bearings.

my idea at the moment is to use threaded rod and make a delrin or nylon nut, use some ball bearings at either end and see how that works out. i understand that direct drive of a threaded rod will limit my feed rates but i am thinking i might try to gear it somehow, anyone any experience with this method? also i do understand that ball bearings will not handle the thrust loads and that is something i will look into. Threaded rod will work, but with a 1mm pitch its really very slow. I'd recommend you look at TR12x3 (which is around £12/m from Marchant Dice on about 4+ weeks delivery at the mo) if you plan to make your own delrin nuts (you need a 100mm bit of rod to make a tap). Igus also do TR10x3 which may be cheaper but no prices on their site, have to request them (let me know what they are if you do). For 10 or 12mm rod at the speeds you likely to get you can get away with bearing support at the motor end only with a single ballrace and a thrust bearing. Technobots do cheap thrust bearings at 8 and 10mm ID.

on the linear end of things i am thinking of getting some nice straight angle stock, probably alu, and making a linear bearing like i have seen on some builds here.... the idea has been done before and works well if you have the constructional skills

...it will be well into the new year before i put blade to wood because i want to have a clear plan. some people say, "dont think it, do it", but i agree a plan never hurts...even if you dont keep to itlol

[Swarfing]

Adrian

You have done it now you know there is no turning back :clap:. A few pieces of advice i can give you is that sometimes it is better to swallow hard and buy the right thing if you can. When you look at the cheap stuff and it does not work you then look at the next bit of cheap stuff and you end up paying twice. With that you could have just bought the more expensive item in the first place. A good place to save money is the mounts. Why use them if you can tap out the ends of the rod and put a decent beefy screw in? this also helps in that you are drilling smaller holes and better for accuracy. remember that bearings need to go onto turned down rod ends and not directly over the thread (my mistake).

I used the Chinese 5 axis all in one drivers you see on Ebay. these have worked out for me but did take a lot of working out. In hind sight i should have gone for a modularised unit as i am limited to no more that 5 amps.

Good luck!

PS set a date to first cut as it is a good kick up the jacksy when it looms i just made mine by 1 week

[wires]

the reason i am looking at this controller is that i have read that it is quite easy to blow a stepper driver, particularly when you dont know what you are doing. with this board that only means you need the driver board and not the whole thing as is the case with single board units.

power supply wont be a problem. like you said, will just keep an eye on the bay from now on for a deal.

with regards to the linear stuff i have come to the realisation that this will not be my last cnc machine. what seems to be the norm here is that you build your first machine and use that to build your second. i know my linear idea is tricky and will take some time to get right but i have lots of time now and i do have lots of patience to get it right. also i am pretty handy with the table saw and router. when i get it modeled i will post some pics for feedback.

i like that TR12x3. the price aint bad either, i might just go for that. it seems i will have to get the ends turned down to fit bearings and coupler. i will have to find someone local to get that done, might know a guy.

i had a good look around the dryline site but i cant decide which size rails and bearings i need. guess thats just my lack of mechanical training.

with reagards to 2e0poz points i do see the logic in buying the propper stuff and under normal circumstances (have a job) i would definatly just spend the £500 on linear bearings and be done with it but i really dont have the cash at the moment. that might change in the future but for now this idea of mine wont cost much to try. i already have mdf and i have a load of ball bearings which might do the job, all i need is some alu angle and a lot of time (being unemployed, time is not a problem). i am not sure i know what you mean about mounts, could you elaborate?

the reason for not doing any construction right now is there is no point in cutting a load of mdf only to find the design change and stuff going in the bin. in my mind its better to just get the design finalised and then as 2oepoz says, you get it made in less than a week.

i can see the advantages of propper linear bearings but i just cant afford them at the moment plus i am not convinced they would really make that much difference to my machine given i will just be cutting mdf or ply. assuming i can get my the home made linear tight engouh and pay close attention to minimising chassis flex i think it will work out fine.

like i said this is my first machine and it will have specific uses. no doubt i will make another more elaborate one soon after this is completed and if i have a job at that time i will put all the propper stuff into it.

thanks for all the advice guys even if i dont take all of it, its just a budget thing. i am getting pretty excited about all this, keep having ideas flying around my head. cant imagine what i will be like the day i fire her up

[irving2008]

i like that TR12x3. the price aint bad either, i might just go for that. it seems i will have to get the ends turned down to fit bearings and coupler. i will have to find someone local to get that done, might know a guy.

You can turn them down with the help of an electric drill, a file and some emery paper and a couple of 12mm ID ball races in some MDF pillow blocks. Support the TR12x3 in the pillow block bearings, suitably spaced, the one at the business end leaving say 50mm showing. Chuck the far end in the drill and whizz it at 1000rpm, then use the file to shape the end to a near fit and finish with the emery paper, doing trial fits on the appropriate bearings or measuring as you go...

You might find the use of a grinder to take the hardening off the surface helps, a dremel or similar is an alternative to a file and can be quicker...

At least one member has used this technique successfully...




Of course if you know a man with a lathe...

[wires]

i have been trying to think how i could do that myself, that sounds simple enough. i have a bench grinder and vernier calipers.

i do know a friend of a friend who works in a tool making workshop, might see if i can call in a favour when the time comes.

being a noob i am not sure what a pillow block is. do you mean a small square of mdf with a hole for the bearing? you then make a hole larger than needed in the machine chassis so that the pillow block can be moved to line it up perfectly?

also, if i am going to get some thrust bearings i need to understand them a little. my understanding of thrust bearings is that they handle the load laterally along the length of the screw but they have no ability to handle side to side loads. do i need a ball bearing and a thrust bearing in each pillow block or am i missing something?

[irving2008]

...being a noob i am not sure what a pillow block is. do you mean a small square of mdf with a hole for the bearing? you then make a hole larger than needed in the machine chassis so that the pillow block can be moved to line it up perfectly?

A pillow block is just a bearing mounted in a carrier, usuall cast or pressesd steel with ears to bolt down with. you can buy them ready-made or, for this purpose, two 12mm id races mounted at equal height in some blocks of MDF screwed to an MDF base will suffice... its only to provide some support for the leadscrew while its being worked on so moderate accuracy only needed...

also, if i am going to get some thrust bearings i need to understand them a little. my understanding of thrust bearings is that they handle the load laterally along the length of the screw but they have no ability to handle side to side loads. do i need a ball bearing and a thrust bearing in each pillow block or am i missing something?

For the actual machine you need a bearing block which retains the leadscrew radially (ball race) and axially (2 x thrust bearing), alternately you'd use 2 x angular contact bearings but these are hard to find in small sizes. See the pic for a guideline

[wires]

ah i see. so if it is supported by thrust bearings either side of a ball bearing on the drive side of the screw there is no need for a thrust bearing on the other end, just another ball bearing. i think if i am going to go that complex on the machining of the ends of the screw i will just get someone with a lathe to do it right.

thanks for clearing that up for me, i was wondering how exactly i would do that. one more thing decided