Design help needed for jig

[idris]

(First post, so be gentle with me.)
I'm trying to build something a bit like a mini rounter table / mini milling machine, (but not actually either of those) and I need some advice on construction. I think it loosely falls into a similar category as fence guides, mitre guages, and router jigs.

I basically need a table (probably about 12" x 12") that i can move acurately in two directions. and something like the chucks of a lathe that are mounted on the table and can be acurately rotated. (By acurately I mean about 0.5mm linear and about 1 degree of rotation.)
(I'd post a picture but apparently "my account does not have permission to post links or domain/page references.")

Before today I was just expecting to use pairs of aluminium U-channel (like B&Q sell) turned on their sides and something like a sheet of HDPE (from eBay) to run within them. Courtesy of browsing this forum, today I have stumbled across T-track from companies like Axminster, Dakota and Incra. But so far I've failed to find much in the way of fittings that would slide acurately within the T-track, other than nuts and bolts. How well do these nuts and bolts fit in the T-tracks or is there something else designed to do the job?

And I'm really stumped when it comes to getting something rotating by increments acurately. So does anyone have any suggestions.

(I have hand tools only and no significant budget, so this is largely dependant on ingenuity.)

 

[Dibs-h]

It sounds like you are wanting a mini 2 axis cnc setup.

http://www.cnczone.com/forums/index.php might be a good starting point.

HIH

Dibs

 

[idris]

Had a look at quite a few of the DIY CNC designs and none really fit the bill.
As I said, it's neither a milling machine nor router table, but the T-tracks that seem to be used dot router tables seem to be what I'm looking for it I can find something that'll slide along them well.

 

[Oryxdesign]

For that size you could use bearing drawer runners.

 

[ossieosborne]

As Simon says, ball bearing guide rails. B & Q do quite a range of sizes in "Keyboard" and "Full Extension" drawer runners.

Oz

 

[Dibs-h]

Had a look at quite a few of the DIY CNC designs and none really fit the bill.
As I said, it's neither a milling machine nor router table, but the T-tracks that seem to be used dot router tables seem to be what I'm looking for it I can find something that'll slide along them well.

Yes but you want the table to move accurately in 2 directions with an accuracy of 0.5mm - to my mind that's a 2 axis cnc bed, although perhaps minus the stepper motors or electronics.

Have you any links or sketches of the sort of thing you want to make?

Dibs

 

[beech1948]

It may be that you will need to build the two axis movement in two parts. An upper plate for the L to R movement and a lower plate for the Front to back movement. Obviously one mounted on top of the other.

Trying to use kitchen drawer slides for this would not provide the 0.5mm accuracy as they have in built slop which makes them work well for drawers but not for such accuracy. You may be able to to use a hammer and punch to "adjust" these runners but it will be hit or miss as to accuracy.

For runners/bearings you might consider two sets of metal bars in bronze bushings. Two sets because of two plates one L-R and one F-B.

Have a look at this web site for some of the tools built by others woodgears.ca.
http://woodgears.ca/reader/index.html

regards
Alan

 

[idris]

Thanks for all the help.

Had a look at drawer runners and Alan is right - they're pretty sloppy unfortunately.
Dibs, fair point, it does sound like a milling machine, but a milling machine and a router table are pretty close cousins ... and I don't want a milling machine. As for diagrams, as I mentioned, my account won't let me post links to pictures.

Maybe I gave too much information, as the question I wanted asking remains unanswered:
T-tracks that seem to be used for DIY jigs and guides: how well to T-nuts fit in them and, if they're not that snug, are there some sort of sliders that do fit well? I assume mitre jigs need to be pretty acurate so I'm hoping the T-tracks and fittings are too.

 

[beech1948]

Maybe I gave too much information, as the question I wanted asking remains unanswered:
T-tracks that seem to be used for DIY jigs and guides: how well to T-nuts fit in them and, if they're not that snug, are there some sort of sliders that do fit well? I assume mitre jigs need to be pretty acurate so I'm hoping the T-tracks and fittings are too.

T-tracks also suffer from the "sloppyness" syndrome. Often devices which use T racks have a secondary means to tighten them up for more accuracy. Example some have a runner ( say 12" of steel) which has small nylon screws along it's length/edges to enable the user to adjust tightness. That will work for a while but will eventually wear.

T-tracks are cheap so maybe buy a 4ft length and some bolts with a head too large for the T-track and then file down the heads to just fit and slide. I doubt you could buy them with an interference fit though. I'm not sure if they would slide but maybe use of a PTFE lubricant may give enough movement and sliding ability. Certainly worth an experiment or two.

Two thoughts come to mind. 1) You could buy from ebay or APEX auctions ( an industrial auctioneer of tooling and machines) a milling machine bed. 2) I recently saw them selling some machine vices which were able to hold a 12" square piece but could be swivelled. SEcond though was something like these.

http://woodgears.ca/mortise/thomson.html
http://woodgears.ca/mortise/lyman.html ..machinists cross slide based machine
http://woodgears.ca/reader/brians_mortiser.html ...shafts with bronze bushings v.accurate

Lets know how you get on. I'm intrigued to know what you are working on.

Alan

 

[idris]

Thanks again.
If tracks are also sloppy, how can a mitre guage ever hope to be acurate? (Obviously I'm missin some critical piece of knowledge here :roll: )

 

[Oryxdesign]

How about two wheels on each corner cranked over at 45 degrees resting on a tube?

 

[Tom K]

I think with six posts under your belt you should be able to post pictures. I seem to remember one manufacturer had sliders with a lash adjustment. Incra maybe?

 

[beech1948]

Idris,

I think the issue is the accuracy you want. 0.5mm or less with T-Track may be hard to get to. In fact 0.5 mm is not very accurate at all.

The DIY CNC world has a few lessons to teach. They could provide two sets of parallel tubes at 90 degrees to each other with the surfaces attached via skate board bearings. You would not need the anti-backlash nuts or much else that DIY CNC uses just the rails and bearings and bearing holders. The bearing holders could be just angle iron or angle ali, the tubes could be cut from a 6ft length of say 2 inch tube. You would be stuck with a L to R set of bearings and tubes and a F to B set to convey two platforms to give you X and Y axis movement.

That may turn out to be your cheapest option which would give you accuracy. Especially if you are placing a chuck on the upper platform.

BUT its worth seeing if you could manage with T-track and could construct a sliding arm which would give you close enough tolerance. The sliding arm could just be 12" of steel cut to be a tight fit into a 3/4 inch T-Track. After you get it to fit and slide then get a pointed punch and a hammer and punch the top of the sliding arm say 1 inch from each end to see if you can cause a bulge to tighten it all up further but still slide. I do this in my Router table about once every 18 months to adjust my steel slider arm in the T-track.

regards
Alan

 

[idris]

Thanks Alan.
For the record I've spent some time researching the DIY CNC type set ups. I was interested in T-track as it is potentially a simpler way to skin this cat and a lot of the DIY CNC designs would benefit from a drill press ... which I neither have, nor have room for.

 

[beech1948]

Idris,
You live in Hertfordshire thats just north of Berkshire...I have a drill press and could help maybe. Send a PM if interested

Alan