There are plenty of X-Y tables around, available from the usual suspects. For example, Arc Eurotrade (catalogue distributed with this month’s MEW) has 3 sizes of table on page 43 of the catalogue; he smallest has a table 200mmX90mm and a table travel of 130mmX70mm. These are manual tables, but would be simple enough to convert to stepper drive if you so desired, using the existing leadscrews.

 

Regards,

Tony

Hi Stephen

 

Can we assume that 0.10mm means that you are looking to maintain positional accuracy across the table envelope of + to – 0.005 mm or better? The problem of part interchangeability and co-ordinate tolerance needs to be factored into any production run unless you are prepared for selective assembly of parts and some scrap parts.

 

You will need to think very carefully about the above tolerance requirements as you could quite easily get into the area of servos that use linear scales as feed back elements. This would vastly increase the cost of the table. For clock making the co-ordinate tolerances are relatively relaxed as the gear centers are run with a very loose mesh as the need is for minimal friction. Backlash in the gearing is not an issue also the speeds are very low so noise produced by a loose mesh is not relevant. Clock makers also use gear tooth forms that are designed for minimal friction unlike engineering tooth forms that are designed to provide smooth rotational transmission of torque, low back-lash and quiet running.  Make a clock with this sort of gearing and it will require too much power to be viable.

 

The simple table pointed out by John Stevenson would probably achieve all that you need for both clock plates and gear wheels. The actual weight of that table would help with getting the required fine finish on the gear tooth profile with out too much polishing.

 

The backlash is simply controlled by approaching any critical dimension from the same direction each time. Easy to do the CNC as it will repeat the direction each and every time in stead of getting fed up with the extra handle twirling! There would remain the problem of lead screw wear and this is one reason to convert to ball-screw drive. The dove-tail wear should be relatively low provided you use a lubricant that is designed for slide-ways. This oil is a specialty oil designed for minimal stick slip and the constant reversal in direction of travel. If the production run is long then the linear bearing skates and matching rails would be required. These are expensive and result in a loss of usable ‘Z’ axis travel. The round rod type of linear slides unless very carefully designed could give you rigidity issues due to the construction of the insert bearing.

 

Suggest you fix the co-ordinate tolerance you need then look at the accuracy obtainable from the various table axis drives then look at how much each design costs. Then revise to get a good working solution. I would go for the simple table with dove-tail slides and stepper motors as I think this will give you the repeatability required for clock making. Convert to ball-screw if the lead screws wear out and modify the CNC tool paths so that each critical dimension is approached from the same direction each time.

 

Hope this helps to get you cutting brass – Regards – Pat