Asking for assistance from a nearby ME, question....

This forum is an incredibly resource for online help and advice on almost any subject. OK some threads wander a bit but often the wanderings themselves are really informative and I personally have learned a lot here.

Occasionally members here do offer actual physical help to a fellow member when they the people concerned are located near enough to each other and when one person has some facility or skill they can impart of offer, like a larger lathe or a spark eroder for example.

I was wondering whether there should be a forum section for members to ask for assistance (free/paid, or whatever) so make the task of accomplishing difficult tasks possible.

Obviously I have an ulterior motive! I need to machine an O ring groove in a rectangular shape in some Delrin. Doing this without a rotary table is possible (but I don't have one) so what I really need is a small CNC milling job doing, I there anybody in the Cheshire area who I could discuss this with?

Regardless of my requirement, I still think there might be some mileage in the idea.

Ian P

Hi Ian,
I do not think a new section is required as I'm sure many members would offer help if the OP could be bothered to give some idea of their location as you and I do. I do not have any CNC milling capability but I do have a rotary table.
The Mill I have is a Seig X3 and the rotary table is a 6" one. I am prepared to help if my mill and rotary table is large enough and you do not get any offers of help from anyone closer.

Les.

Les, you are right about people not giving their location but I doubt its because that cannot be bothered, more about not wanting to give personal details (although a county or a town is hardly personal!). Sometimes the poster might be asking about where to buy something, its pretty pointless anyone replying without even knowing which country the question came from. (Rant over)

Thank you for your offer. I did state correctly that I don't have a rotary table in the accepted sense. I do have a thick aluminium disk mounted on on old automotive front wheel hub that I can rotate manually and with lost of jigging around can index or rig up end stop positions. The groove I want to do is about 3mm wide and 3mm deep in the endface of a 12mm wall thickness rectangular tube which is about 150x180.

To correctly get an accurate transition from the straight sides to the radiused corners will require an awful lot of setting up whatever the rotary table is like, and I want to cut two of these grooves.

Without CNC what is really needed is an X-Y table mounted on a rotary table, not that I have ever seen one setup like that. Even then the potential to turn one handwheel the wrong way once makes getting it right first time very unlikely for me!

I did get a PM from another (non local) CNC equipped forum member which I am investigating.

Ian P

Can be done using the DRO if you used the ARC function at each corner but could be a long slow process depending on how many increments you selected to get round the corner but if you don't have a R/T you probably don't have a DRO either.

J

I have a DRO but it is dumb so has no arc function, however I suppose I could generate and print out a list of coordinates to manually drive the cutter round the corner curves to do the rectangle, perfect recipe for a disaster though!

Ian P

I see what you mean.

I have not watched any of the Youtube videos but I imagine that setting one up would be good fun. Bring on CNC!

Ian P

imho, you are perfectly equipped then...

Rgds, Frank

i dont think it would be that difficult depending on size.

ive got quite a range of 'round headed' dental burrs going up to about 1/8" and 5/32"dia. it would be quite easy to do the groove for an 'O' ring with these on a mill or vertical slide. i can tilt the head of my mill to get a deeper groove.

cheers,

julian

Cutting the groove is the easy bit, its following a rectangular path with its rounded corners that is the harder bit.

Ian P

Hi Ian,
My initial assumption was that the groove was circular in the end of a solid rectangular section. My understanding now is that the groove (Or grooves.) follow the sides of the rectangle and are joined at each corner by a quarter circle with a fairly small radius at each corner. Here is a suggestion. in the opposite end of the section to the groove either drill a small hole at the centre of each corner radius or attach a plate with holes in these positions. First mill the straight parts of the groove. Then clamp a plate to the mill table with a pin sticking up to engage with the drilled holes. Position the pin at a distance equal to the radius of the corner grooves away from the spindle axis.put the work piece on the plate with the pin inserted in each corner hole in turn and clamp two strips to the table to limit the movement of the work piece to 90 Deg. With the aid of an assistant it should be possible to hold the job down by hand and swing it through 90 Deg. as it is only made of delrin.

Les

I'm just a 2 minute drive east of Sheffield if your passing and have a 3 axis CNC mill, happy to help, check your PM!

Thanks to all who offered advice and help with this problem. More than one person has offered to cut the groove for free which I am really grateful for. One member did not reply here, but PM'd me and I have actually posted the lump of plastic to him.

Russ, I have PM'd you but thank you for your kind offer.

Les, I have used your method on previous occasions but usually only for a simple single radius type of job. I did not fancy doing four corners and getting the groove width and positions of the straights and curves anywhere near right without a lots of material to practice with. I have usually hand held and hand fed the job whilst rotating round a pivot pin. With care

Frank, I deserved that. Dropped myself right in it there!

Thanks all

Ian P

No trouble Ian and thank you, always free help at my end in the rare cases I can help out!

Could you not wrk out the outside dia of the corner radius, and make a single point tool this size? You would only need X&Y moves then to achieve the correct profile.

Found this on Ebay last year going cheap because no one knew what it fitted.

Well it fitted my Bridgy once I'd thrown the weird mounting away and welded a new tube mounting up.

It's German Wako unit which is a lot like the volstro heads and can move in arc and straight lines either independently or together if you can get your head round the maths.

Personally it looks better on the mantelpiece and use the CNC for hard bits.