Changed pinion gears. Now what????

[jzarski1]

Since I am still nursing my finger I figured it's a good time to get some friends to help me do some general maintenance on the Bot.

Put the new pinions on and I am not sure if there is anything that I need to do before running it? How tight do the springs need to be? Do I need to put any grease on the racks?

John

[ron_moorehead]

My understanding on how tight the springs should be, is to get them just so they start to be tight and then three full turns on the turn buckle, and yes grease the racks.

I just bought new pinion gears to do the same thing. But got some bad gears I think. No keyway or set screws in the gears.

[jzarski1]

Mine had set screws, but no key ways. The old ones where a pain to get off. Not sure if that is normal but it was not fun.

John

[paul_z]

John,

There may have been two set screws in each hole. If one has the depth, it's a good way to make sure that the bottom screw doesn't work loose.

Paul Z

[jzarski1]

Ok, now I need help big time. I have the new pinions on. I ran the machine for the first time with them and I have issues.

1. The cuts look like poop... Tons of tool lines and scallops.
2. Much more vibration and noise.

I spent all night fussing with it with no valid results. I tightened the spring, I loosen the spring. Moved the pinion in and out on the rack. Changed the jog and move speeds. Nothing seems to fix it.

I am at a lost. Please if anyone has any ideas let me know. I have a ton of parts that need to go out and I just hired someone to run my machine while I am still nursing this finger issue. Thanks in advance

John

[bleeth]

John: Often the issues you are describing come from a couple of places. As this PRT is new to you it is important that you have everything square, level, and tight. The racks need to be properly greased (Lithium works well). Squareness of the gantry can't be emphasized enough. With the motors turned off and unplugged slowly roll the gantry up and down the track. All the wheels should be in constant contact with the rail and nicely centered at all times. Do the same thing with the Y car.
I noticed you mentioned from the time you got the machine that it wasn't giving you the cuts you expected.

A standard PRT has limits on the feed and speed and if everything is properly dialed in you still may be exceeding the capabilities of the equipment. What are you cutting, what kind of bit, what feed and speed? Do you have a router or a spindle?
The more full your reply the more others can help.

Where in central Florida are you? I know someone in that area who may be able to come by and help but you need to e-mail me your contact info (left click on my name and select send e-mail).

[jzarski1]

A standard PRT has limits on the feed and speed and if everything is properly dialed in you still may be exceeding the capabilities of the equipment. What are you cutting, what kind of bit, what feed and speed? Do you have a router or a spindle?
The more full your reply the more others can help.

Where in central Florida are you? I know someone in that area who may be able to come by and help but you need to e-mail me your contact info (left click on my name and select send e-mail).

Hey Dave,
I am cutting .5" MDF. My cut speeds are set to 2.5ips, sometimes I cut at 3.0ips. There is no change between those two speeds. I use a down spiral .25" endmill. I ramp in the first cut with a depth of .4" and a .001 offset. The final pass is .112" with no offset. I have a Colombo spindle with the VFD. I cut at 8000 to 10000 RPM as this makes the best sound when cutting. Anything above the 10k I get high pitch squels.

I am located in Palm Bay Fl. I will send you an email right now.

John

[bleeth]

John-check your e-mail.

[jzarski1]

Well I am still trying to figure this issue out. I am posting a like to a video I took. Turn up the volume and listen to the machine. It doesn't sound right to me. If I wrong and the sounds are normal then where do I need to look to fix this chatter issue. There are two videos of the bot running, I am posting one the other one can be seen in my profile on YouTube.

http://www.youtube.com/watch?v=Ig5LotHgWj4&feature=youtube_gdata_player

John:confused:

[Brady Watson]

You are running 25 tooth on X&Y and 20 tooth on Z, right?

Are you running DOS or SB3? If running SB3, what's your VR value screen look like? (Bring it up & do an Alt+PrntScrn & then paste into MSPaint & post here)

Also, what's your VU settings? 916.xxx for X&Y? 3G PRT or are you running the 4G? I hear mid-band resonance so it is hard to tell.

-B

[jzarski1]

How do I know if it's a 3G or 4G.

[jzarski1]

Here are the images. I have the 4G board.

http://i576.photobucket.com/albums/ss210/jzarski/27dea7ea.jpg

http://i576.photobucket.com/albums/ss210/jzarski/073b0b32.jpg

http://i576.photobucket.com/albums/ss210/jzarski/f7c5f577.jpg

John

[Brady Watson]

Type in the UR command, hit enter 3 times, and pick your tool from the list. If it is a 4x8, select PRT48964G under Older ShopBot files.

Your VU on the Z is incorrect & the 1st 2 parameters of your VR should be .4, not .25, and move ramp rate should be .2 - UR will fix it all.

-B

[jzarski1]

If the VU is incorrect on the Z then wouldn't my Z height be off? If so its not incorrect, my Z in spot on.

John

[Brady Watson]

What does red & silver Vexta nameplate on the Z axis motor say - 0.25 or 0.5 deg step?

How many teeth does the Z axis pinion have? It should be 20, unless your tool was originally setup for foam cutting only.

Regardless of what the VU is, the VR settings are less than ideal.

1st 2 settings should be .4 (I can hear the sluggish acceleration in your tool because of this...)
Move ramp rate should be .2 (This will tighten it up some)


-B

[jzarski1]

The motors are 0.5 deg/step. Not sure how many teeth the Z has. I have never taken it off.

[Brady Watson]

There should be a 20T pinion on the Z. That motor is 3.6:1, which means with a 4G board, your unit value for the Z should be 2291.xxx - Doing a little math it shows that you are running a 25T pinion on the Z. You're losing 20% torque and resolution on the Z by running a 25T pinion. It's the not the end of the world, but not exactly ideal for machining wood and plastic...so keep in mind. You can pick up some performance by swapping out that 25T for a 20T.

-B

[ron_moorehead]

Question I just replacement my pinion gears and ShopBot updated me from the 25 teeth gears to a 32 teeth gear saying I would have better resolution with the 32 teeth gears and that the 32's are standard on all Alpha today. But you just said a smaller tooth gear would give you better torque and resolution. I am running a PRT Alpha with the 7.2:1 motors and I updated the unit values to match the new gears. My settings are standard for ramping and so on. I know my pinion gears and set screws are tight and I done the shack test on both the Y and X travel and everything feels tight. My cut on most things are great, cut a circle the circle looks great no chatter at all. But if I cut a square I get chatter on the out ward side of the cut travel. Going into the corner looks fine going out of the corner I get chatter for about 1/2 inch of travel. My move speed was at 1.66 I dropped it down to 1.00 it helped but I still get the chatter. I have been cutting the same files for years now and have not had this problem before. Any ideas. Thanks.

[Brady Watson]

PRT & PRS Standard should have 25T XY, 20T Z

PRT & PRS Alpha7.2 should have 30T XY, 25T Z

I'm not aware of a 32 tooth pinion...maybe you meant to say 30? 30 T pinions are better matched to the 7.2s higher resolution. They have more teeth engaged in the rack than the 25 T do, so they last longer...but the 30s won't give you higher resolution than a 25s.

Your chatter issue could be a number of things, like cutter deflection or your rails need to be cleaned and deburred.

-B

[jzarski1]

Looks like I solved the problem. When I purchased new pinion gears I was unaware that there is two different rack types. I called Shopbot and ordered 25T pinions for my motor model number.:rolleyes: Well to make it short they where the wrong gears. Frank finally figured it out and had three new gears overnighted to me. I put them in today and she is cutting smooth.... Really feel like a dumb #£%.

Brady,
I still have the awful noises coming from the machine so where do I start for this issue. I set all the VR setting back to what you suggested. I am going to order the 20T pinion tomorrow. Know clue why there is a 25 on it. But if you say it is I believe you. You have been spot on with everything else.

John

[jzarski1]

20T pinion is on its way. If I understand the chart Frank sent me I should change my Z values to 2291.831 from 1788.4487
Is this a correct statement?

John

[Brady Watson]

Yes...You can also just reset your config to a PRT4G and it will set the UV for you.

Now...when you get the 20T, it will take you some time to set it up correctly. Pull the springs down off of their perch (make yourself 2 wire loops for pulling them down later) - and remove the t-rail stop bolt so you can lift the entire T-rail up & out of the towers. Next, remove the Z motor and replace the pinion taking care to really crank those set screws down. A 4x4 block of wood will come in handy to set the nose of the router on for the next step. You'll want to slide the t-rail back in & then move the motor to mesh with the rack. Get it close. Then you are going to BE DELIBERATE when you adjust the v-rollers to set the lash on the pinion - don't make the tension on the t-rail too tight or you'll spread the towers and wear out the t-rail. Whatever you do to one, you MUST do to the other 3 (or 7 if you have 8) - so note clock positions of the v-rollers and sneak up on meshing the t-rail rack to pinion - all the while making sure the rail is neither loose or tight. It will take some time, but if you do it right it's a set it & forget it thing. If you run out of adjustment on the rollers, you'll have to move the motor over a little closer to the rack and start over with the adjustments - taking the t-rail in & out until you are happy with how it all moves.

It's not hard...if you are observant - it just takes time.

-B