Checking y-axis backlash/freeplay

[KevinO]

I've tried making a few wooden gears with my new Shark Pro Plus with mixed results. Accuracy is the concern. The gears look great but the center hole is about 0.020 inch oversize, and seems to be egg-shaped in the y axis direction. I used the internal profile in VCarve to cut it. Would pocketing give better results?
I want to check the tightness of all the axis set screws as recommended by numerous posts. Unfortunately, none of the posts I've found offer advice on how to get at them. I hate to remove the bed of the machine to get at the y axis set screw but see no other way.
Can anyone offer some suggestions on how to go about checking the backlash, particularly on the y axis. Does removing the bed invalidate the warranty?

Thanks
Kevin

[FixitMike]

It is easy to get to the Y axis screw. Just loosen the (4) bolts holding the two center table extrusions and slide the extrusions lengthwise. You don't have to remove all of the extrusions.

[Bob]

Kevin,
I have the best success making holes in gears by using the pocket cut. Also, I keep the depth passes to .06". This way, I'm not trying to remove too much at once.
When I need to make .125" or .25" diameter holes I use the drill function, and select peck drilling about .06" at a time.
If I need a really accurate hole, I cut the proper diameter using the pocket function. I only cut to a depth of about .06" though. I then use that as a guide to finish the hole on my drill press.(It's set up for very accurate drilling.)
Thats how I drilled holes for this machine:

Bob

[rungemach]

Hello Kevin

As long as you are checking your couplers, you may want to consider replacing your set screws with cap screws of the same thread size. They take a larger allen wrench and can be tightened with a better feel for the torque. I am attaching a picture of the way they look on the machine as well as a comparison of the wrench size. I have also seen white glue suggested as an anti-vibration aid, rather than regular Locktite. Be sure your setscrews are engaging the flats on the motor and the lead screw as well. It may be a good time to check the other fasters on the machine to be sure all is tight and there is no loose play at any joints.

Once you have done that, if the problems still persist it may be machine flexing under the load of the cut, and a series of shallow cuts at lower speeds will show you if there is a difference in your resultant hole size and shape due to that. On the non HD models, the flex in the Y direction is greater than in the x due to bearing rod flex under cutting loads.

as the other Bob suggested, if the hole size is small enough to be drill-able, I have had good success using a 1/8 drill and just touching the surface enough to make a dimple to locate the hole, then drilling the correct size hole on a drill press. This works great with metals like aluminum,( that I frequently cut). For large through holes I use an inside profile and shallow passes, If you like you can make two toolpaths. one to rough the hole a several thousandths oversize and a full depth finish pass to take just a shallow cut to get to final size. Too fast a cut speed doesn't help either, so keep the feed speed low enough to get the accuracy you need.

Hope this helps.

Bob

[KevinO]

Thanks Mike, once you told me how, it was easy to check the y axis set screw. It was tight so at least I eliminated that as a cause.
Bob and Bob, thanks for the great suggestions on creating accurate holes. I retried by pocketing rather than profiling and measured the results more accurately this time. I used a 0.25 end mill at 10 inch/minute (slow!) with a depth of 0.06 inch per pass. I made an 0.812 inch diameter hole in 0.25 plywood. It measures 0.827 and is not much out-of-round. If it's consistently oversize, I can perhaps compensate by defining the hole as 0.015 undersize.

I think both of your suggestions to create a pilot hole is the best approach for a tight tolerance hole. That's probably what I'll end up doing.

I'm also going to install cap screws to replace the set screws with a touch of white glue for good measure.
Thanks again for all of your help.
Kevin

[Eagle55]

Sounds like you are on track to the solution. Just want to mention something that I have learned from reading post here on the forum (not from first hand experience yet) But the run-out of router collets can be an influential factor of pocket cut accuracy. In other words although the router bit is assumed to be turning perfectly, most times it is not. So if the 1/4" diameter router bit was turning perfectly true it would cut a 1/4" hole if plunged straight into the material. If it has for instance .005" of run out, it would cut a .260" hole instead of a .250" hole. Most of us use something like the Precise Bits collets mentions in the forum. I have bought the 1/4 and 1/8" versions just in case I need the accuracy but also as a way to accurately use a 1/8" shank bit which is not available from Porter Cable that I am aware of. Anyway that came to mind when you mentioned slight oversize routing. To test this theory you can put a bit in the router and set up a dial indicator and see what the run-out is. And try the same set up multiple times... ie take the bit out, put the same bit back in and tighten it and measure runout again. My guess is that you are going to have more run-out than you imagined and its going to be slightly different every time you put a bit in the collet.

Roger

[jeb2cav]

Bob (Rungemach) - thanks for posting the tip on using the cap screws. I've been struggling a bit with the y-axis. Using the cap screws has really improved the outcome (I haven't had to remove the table top and tighten things up since doing this).

Another tip for readers is that when you do this, apply pressure on the gantry away from the motor. This will fully seat the y axis (or any axis) in the support bearing, and remove any freeplay between the motor/lead screw/support bearing. You will notice a dramatic improvement in v-carved letters in particular...

There should be no 'clicking' or 'clanking' noise when you press gently on the gantry or router mount. If you hear such a noise, taking the time to service this coupler is well worth it. I knew that part, but so far, the cap screws with wood glue has been the silver bullet.

[Larry Gardner]

What Size are the Cap screws that you guys used??? I had my X-Axis set screw loosen up on me yesterday and was thinking of replacing all of them with Cap screws...
Thanks

[rungemach]

I used 10-32 x 1/4" long cap screws.
You can also use 1/2" long if you can't find 1/4" locally.
You will need to shorten the 1/2" long ones on a grinder or sander to clear the outer hole they must fit into.

Couplers may have changed, so best to double check your thread size.

also, be careful when tightening, as you can put so much torque on them that you can strip a coupler's thread if you get heavy handed.

bob

[REG]

You can solve your setscrew problem by changing the coupler. I recommend the split type coupler. It squeezes the circumference of each shaft end rather than press at a single point (setscrew). You can pick these up on ebay, McMaster Carr and other automation suppliers. The one pictured is aluminum but you can get them in brass, and machined tool steel.

Bobby