I have been battling this slop for awhile.

[knight_toolworks]

I have replaced all the rack and pinions on my prt alpha and everything seems tight. this is a cut the first pass is with a 1/4" downcut at 3ips 10k rpm .45 pass cllimb and a cleanup pass at 1.5ips usually the part comes out right but there is so much slop not always. anything above 2ips gives me a fair amount of slop sometimes. I don't find any more slop then usual when I tug on the machine there is a little in the z that I have not dialed out. I am wondering if it is a ramping issue? my software crashes and the settings get reset. so they may not be right.
http://www.talkshopbot.com/forum/attachment.php?attachmentid=29655&stc=1

[Tim Lucas]

Not sure but you are using a down cut and cutting .45" deep I think that may be a problem - I don't have a alpha and I use a compression bit 1/4" and I am pushing it to cut .3" @ 3.5" sec. I would think you need a 3/8" compression bit.

Also you say your Z has a little play - is it in the direction of the slop??

maybe somewhere to start

[guitarwes]

I have a PRT Alpha. I cut 1/2 and 3/4 plywood with a full depth pass in a conventional direction using a 1/4" compression bit at 4ips at 204.7Hz.

[Gary Campbell]

Steve...
The items that can be related to the slop you show are listed below. In some cases they are a maintenance adjustment, in others normal wear and tear associated with long term use.

Z axis:
Wear of the Z axis slide assembly outer "V" surfaces
Adjustment of the Z axis roller bearings (and 4 vs 8)
Condition of the pinion
Grub screw adjustment
Proper pinion to rack adjustment

Y axis
Condition of the horizontal portion of the Y rails
Adjustment of the rollers that ride on the horizontal portion of the Y rails
Condition of the rollers and rails
Condition of the Y pinion and how secure the grub screws are
Proper spring tension
Backlash present in the gearmotor

X axis
Condition of the rollers
Condition of the X pinion and how secure the grub screws are
Proper spring tension
Backlash present in the gearmotor
Condition of the V rails

Your issues can most certainly be solved by some combination of adjustment, replacement or repair of one or all of the above.

[knight_toolworks]

I was cutting too fast about 2ips with that depth on baltic birch and the slop was a lot less. plus the bit was a little duller then I thought it was. though it used to be not be as critical. the pinions are new last year and the racks are new too. but I need to check the rollers in different places . when I push on the machine I don't feel any more slop then usual. but thats when it is is at 0. When I cut some more today I slaw a lot of slop in the climb cut with a fresh bit but not as bad as the pic. going to 2ips took most of it out and got it back to normal.

[bleeth]

Quick response to add to Gary's is to your statement "pinions new last year". You are much more than a light user. Last year runs from just a little over a month ago to a full year. Heavier users should change pinions at least once a year. Unless you are running the 1:1 Alpha motors you should be getting a good clean cut 1/2" deep with a good 1/4" bit in BB faster than 2ips. Could be time for that all over tuneup from cleaning and grease to complete verification of squareness, z-plumb and all bolts. A day or so of that at least once a year can work wonders,
FYI: My strategy for my PRT when it was a standard with Gecko drive was 2.5-2.75 in plywood with 5mm" at 3/8" deep and it was smooth enough to go straight to the edgebander with no sanding. With a PRT Alpha with geared motors you should easily hit 4ips that deep with 1/4" and have sweet parts. Your issue could be a compound of several ingredients all contributing a little.
(Wish you were on this coast-Now that mine is sold it would be fun to be tweaking and tuning yours with you!)

[knight_toolworks]

ya I a sure it needs abetter turnip. found one wheel on the horizontal part of the carriage that was free turning. but it would not move enough to make contact. the opposite feel did on that section of the rail. so is the wheel off or maybe the carriage off a bit? I get around 2 years on pinions and I usually tell they are worn when I pull and push on the machine when it is on. I checked and they were changed a year ago. the racks were all changed in October or so. I sometimes push bits too far since I seldom cut one thing long enough to dull a bit it is hard to keep track of the wear on a bit.

[bleeth]

Whether it is a roller from the z car to the y carriage or the y carriage to the x rail if you have one not in contact you have an issue that will cause sloppy cuts.
Since the PRT's y's and z's are bolted frames they can get out of square/alignment over time to the point where there isn't enough movement in the roller adjuster to square it back up.
Sounds to me like you are ready for a major tune-up. Pretend you just bought it and set it up and now it's time to start dialing it in beginning with verifying square and level of the x rails and going on step by step from there. Check every bolt and make sure your x rails are still straight and true. If you actually take the time to go through the whole thing I bet you'll be amazed!

[knight_toolworks]

mine is the one piece y carriage. so it would be pretty bad if it was warped. but a little fiddling and I got the wheel tight after I used a needle nose pliers. I need some thinner wrenches. so I can adjust the z wheels.

[knight_toolworks]

the first thing I always check is loose pinions. I was replacing a split dc hose and found the y pinion loose. This last batch of pinions have too small set screws and you can't really tighten them down enough.

[jerry_stanek]

mine is the one piece y carriage. so it would be pretty bad if it was warped. but a little fiddling and I got the wheel tight after I used a needle nose pliers. I need some thinner wrenches. so I can adjust the z wheels.

When you say a one piece carriage is it a PRS I had to loosen all the allen bolts on one side and the end plate settled down on both rollers

[knight_toolworks]

the prt has a one piece frame with attached rails well the newest version had it. . but I got the wheel adjusted. but then I found the y pinion loose even though I just checked it yesterday maybe because the machine was cooler. the last set of pinions came with much smaller set screws and you can't tighten them down as well.

[Dish]

Use loctite on them.

[knight_toolworks]

I did but they are small enough the Allen wrench twists. they are smaller then usual so you can't get the tool to not bend trying to tighten them.

[ken_rychlik]

I gave up the fight and bought a ball screw machine. It's not perfect, but the problems are much smaller. On the first prt I had, I welded up all the bolt together sections, then bent them back straight from the welding, and added a bearing on the Y opposite side of the motor along with a spring to pull that side tight to the gantry. It did help a lot.