Tips collected from the Shoptask forum.
Sorry for not tracking who submitted what.
If you have trouble adjusting your gibs enough to take out the slack, but still have free handle movement, you may have a slight bow in the gib strip. This has happend a few times over the years, when the factory guys stamp the serial number on the gib strip- if they dont have it on a flat enough surface, the number stamping can warp it. Its easy to fix, just remove the strip and lay it on a piece of sandpaper on a flat surface. You will see by the shiny areas if you have high and low spots. Just work it down until its even on bothe side- a belt sander makes this a 60 second job. Clean it good and be sure to touch the edges as well. We reccomend this for all cnc users before ding your software setups.
On tip on polishing the gibs. After an hour or two of trying to hang on to them with my fingers I got smart and machined a small pocket in a 1"x1"x12" block of wood for the gib to set in. Made the job a whole lot easier.
Q: I am new to this and need some help. I do not get a good finish using
the small flycutter on aluminum. I have tried different speeds and feeds,
I am still not satisfied with the finish. any suggestions?
A: Chances are the "heel" is dragging. A common cause of what you described.Make
sure your tool has 5 to 7 degrees clearance
and grind/stone a very tiny radius on the tip. .015 r
Also make sure the splindle lock lever is just tight enough to hold
the spindle firm and still go up and down. so It won't "bounce".
Locking it down tightly at depth is a good Idea.
Bench design
For an average height guy, bench top should be about 32" from floor-top
size should be 24X48 minimum, and be sure to allow 24" free space on left
of machine to open door to gear system.
Having casters on the bench for ease of moving the machine is a good
idea.
Backlash
When I initially setup my Shoptask CNC machine, I was able to get the
X axis backlash down to about 0.008" by adjusting the ball bearing preload,
tightening the brass nut set screw and tightening the CNC drive gear set
screw. After very little use, the backlash was up over 0.030". The two
problem areas were the CNC drive gear and the brass nut.
E-mail with JT revealed that on the machine in his shop the CNC drive
gear had been modified to have two set screws (in line) to engage the flat
on the x-axis lead screw (mine only had one set screw). Because of the
position of the current set screw, I did not feel comfortable adding another
hole along side of it. What I did was to drill two new holes displaced
90 degrees from the original and with three set screws, hopefully that
problem will be solved.
I still have concern with the brass nut. It seems we are asking a lot
of the small pointed end of the set screw. Since the brass nut is about
0.015" longer than the steel holder, I am considering adding two plates
(that would be attached by 6/32 cap screws) to the end of the steel holder
to sandwich the brass nut. I would retain the set screw to prevent rotation
of the brass nut while the end plates prevent horizontal movement.
The set screw for the brass drive nut should hold it under normal loads,
however, for those crashes, it can be a life saver- Tim is running a 5
amp system, so his drive power is a lot- even our standard 2 amp system
will drive the brass nut right out of the bracket if you run the carriage
up against a stop. Locking the nut in place with plates on each side will
be fine as long as no crashes occur, but if they do, then some bigger components
are going to have to give.
There are a couple of other things that cnc and even manual guys can
do to reduce lash in X and Y-
On X, get a piece of 5X5 angle iron and wrap it around the drive bracket
and secure it with screws to reduce flex in this bracket under loads. You
can cut it to fit with a band saw and paint it to match-
On the Y you can modify the bracket on the handle end with torrington
bearings, so that you can take all the lash out of the screw/bracket part
and make it real smooth-
Metric torringtons are available for about 5.00 each- and you just
relieve the bracket on front and back enought to accept them- Obviously
you need to run the Y axis while doing this if you use the lathe , so you
can just make a temporary bracket out of 1/2 X 2" flat bar while re-working
the original. If you use the mill, then you can position the Y by hand
and lock it down.
I seem to have a lot of slop on the fine feed handle of the Z axis.
I was wondering what everyone else is seeing as normal movement of the
fine feed handle before the quill starts to move? On my machine I get about
1/2 of a turn on the fine feed before the coarse feed handle starts to
move.
At first this movement was even greater, then I noticed that the fine
feed dial allowed excessive end play on the fine feed drive shaft. After
replacing the slotted set screw in the fine feed dial with a proper allen
head set screw I was able to get the fine feed shaft end play to hold at
the tighter clearance I set. This helped, but I am still getting the 1/2
turn of the fine feed handle slop.
Tim
Mine has a full 3/4 turn of backlash. Very annoying. It is also bad
about jamming on the backside of the backlash.
Bill
I had the same problem. I found that the bushing had moved outward allowing
the fine feed shaft to have a lot of endplay. I took the entire assembly
apart, cleaned it and rotated the bushings 180 degrees before reassembly.
I then drilled new pilot holes in the bushings and installed the set screws.
That lasted for a short while, but yesterday I noticed I had excessive
backlash again. The bushings had once again moved outward. I found that
on my machine if the edge of the bushings were even with the housing, I
had no endplay on the fine feed shaft. I again took the entire assembly
apart and this time I drilled two holes into each side of the housing about
0.100" from the edge of the bushing hole. I then tapped the holes for 6/32
allen head cap screws. I placed flat washers under the cap screw heads
(to force the edge of the bushings even with the housing) and tightened
everything down. Almost no fine feed shaft endplay now. Hopefully this
will correct the problem. I also reinstalled the set screws to prevent
the bushing from rotating. If wear causes the endplay to return, I can
place a shim between the end of the bushing and the washers. I also have
as much load on the return spring as I can get to keep pressure on the
rack and pinion of the drill press feed.
John
This adjustment on the Z axis done by Tim is the best way, especially
if you are using cnc- when adjusting up the bushings, always rotate them
and drill new dimples for the set screws. Tim's idea of a screw on the
face is good. One problem that can happen, is if you lock down your quill
and then forget and turn the fine feed handle. The leverage of the worm
gear is a lot and it can force the bushings out- I've done it myself- any
suggestions from the group on how to make the adjustment easier are welcome-
without changing the design of the cast block would be best, as it takes
them a long time to modify those parts.
jt
There is another possible source of lash in the system as well, inside
the block there is a steel pin which holds the worm gear in place and it
goes through a slot in the shaft which allows the worm to slide back and
forth to engage/disengage the worm for drill press function- If the pin
has to much clearance in the slot, then you will get movement before the
worm moves- We are working on a simpler solution to the entire situation,
we now have a unit up and running with a ball screw driving directly on
the quill- so far its working fine, but we want more test time before preparing
a kit for our cnc customers- we have used the standard system for years,
and the backlash compensation in the software is sufficient to maintain
accurracy, but lately we have been getting a lot more people involved in
very fine contour work, and I think the ball screw drive will be a good
option for them, while leaving the standard drive for those who dont require
it.
jt
I finally found the time to pull the Z axis mechanism that engages the fine feed apart to see if I could reduce the horrendous backlash that was present in the fine feed lever. When GL was over visiting he told me about what he saw when he had his apart to change the spindle to R-8 and how he thought the Z axis backlash could be reduced by disabling the fine feed release and fixing the fine feed spur gear directly to its shaft.
Well, I am happy to report that GL was right once again. I tapped 2 6-32 holes 90 deg apart on the non-toothed portion of the brass fine feed spur gear and locked this gear down to the shaft with some allen cap screw. The other modification I made was to put a needle thrust bearing between the fine feed movement indicator and the CNC motor mounting plate and another between the plate and the CNC belt pulley. The thrust bearings have made it so the fine feed shaft does not move end to end at all and combined with the worm spur gear being fixed to it's shaft I now have no noticeable backlash in the Z axis.
If you can live with only using the fine feed this modification will
get rid of the .040 - .050 backlash that seems normal in the Z axis and
the total cost is under $5.00.
Tim
Message posted to the Shoptask forum on Onelist by
I CNC'd my X and Y axis first, then modified the Z axis mounting plate
using CNC. For belt tensioning, I milled some elongated slots for the motor
mount bolts (instead of just holes) and then milled a large slot to allow
the pulley flange to clear. ( My motors have short shafts, so the pulley
flange must go "inside" )
(I would not have liked this task as a manual project - it was trivial
under CNC !)
I considered a solution like Tim's but I like this solution more than a tensioner, as the belt is now surely tensioned the same top and bottom. ( With a single tensioner top or bottom, there is almost certainly slop on the untensioned side.)
I also modified the Z axis feed mechanism to attempt to remove backlash. First step was to pin the brass gear to the drive shaft (no more "drill press" function but so what - only a problem for tapping holes and I have a MUCH better solution to that problem)
Using a suggestion elsewhere in this forum, I added a thrust bearing to the feed shaft, between the pulley and the mounting plate. I eventually used a BALL thrust bearing (instead of a needle) - this turned out to be important.
Next I added another thrust bearing to the other side of the mounting plate, hoping to secure it with the indicator dial. The result was not acceptable. It was too hard to "cinch up" things to take out all the slack. And the set screws just didn't have enough oomph to overcome the force of the worm gears.
Instead, I disassembled the mechanism (again). I drilled the feed shaft and the pulley for a roll pin, to POSITIVELY locate the pulley. I then drilled and tapped the end of the feed shaft opposite the crank for a 1/4-28 bolt. Next I machined up a stepped collar, about 1" long, 1.5" diameter on one end, .5" diameter on the other, through drilled 1/4".
Reassembled.
Another ball thrust bearing was installed on the small diameter of the collar and the collar lightly bolted to the feed shaft.
The crank is turned so that it engages the worm gear and the ball thrust bearing at the pulley is under tension (compression). While under tension, I tightened up the bolt on the other end of the shaft, tensioning against the other bearing, taking up the slack at that end.
The fine pitch screw allows one to set just the right amount of tension, not so much that things wear, enough so that all rotary motion is converted to right angle motion, none wasted in fore and aft movement of the shaft.
At the end of it all, lots of measuring shows .012 lash .. not bad at all, methinks, and a bit of a pleasant surprise.
Alan
Thrust Bearings
I got the needle thrust bearings and the companion needle thrust races
from MSC. These are the same items
I used on the Y axis. JT recommends you hunt down some metric thrust bearings,
but as far as
I can tell these are working just fine.
The part number and price from the current 98/99 big book catalog are
as follows:
Needle Thrust Cage Assembly
.5000 ID #03380904 $2.10
.6250 ID #03380912 $2.08
Needle Thrust Washer
.5000 ID #03381076 $0.62
.6250 ID #03381084 $0.70
For a complete bearing you need 1-cage assembly and 2-washers.
The Z axis took 1-.5000 and 1-.6250
The Y axis took 2-.5000
Tim
Shoptask v-belts.
They are most definitely a metric "Type 10" v-belt, which means they
are approximately 10mm wide by 6mm high. This size most closely conforms
to the English "3L" series fractional horsepower belts, which is 3/8" wide
by 7/32" tall.
An interesting item worth mentioning... metric v-belt lengths are measured
and sized on the *inside* diameter of the belt, where as English sizes
are measured at the *outside* circumference of the belt. So you can't simply
take the known size designation in millimeters from a metric belt, convert
it to inches and order up the same English sized belt. You either need
a conversion chart or you must take physical measurements.
Specifications are as follows (near as I can tell)...
Mill / Drill Head
Factory:
2 each Type 10 metric x 850mm long.
Replacement:
2 each 3L345, which is 34.5" long.
Lathe
Factory:
1 each Type 10 metric x 710mm long.
1 each Type 10 metric x 800mm long.
Replacement:
1 each 3L293, which is 29.25" long.
1 each 3L330, which is 33" long.
The good news is that good quality brand belts from the likes of Gates
or Browning are inexpensive (typically less than $5.00 each). The bad news
is that these sizes are sort of rare (slow movers in the retail trade)
and may have to be special ordered from the supplier of your choice. I'm
sure Shoptask must stock metric replacements if you're ever in a hurry.
John L.
We have the original replacements, but just use them for warranty purposes-
The quality of the Chinese is ok strength wise, but they do not clean the
flashings left from the manufacturing, so they tend to throw a lot of black
stuff around when new. Use the 3L series belts, but the even numbered sizes
are common and work fine-3L 350, 3L280 etc. its the 1/2 sizes which are
usually hard to find.
jt
Tool Post Hieght
I remember reading of someone else with this same problem and was wondering
how common it was. I ended up having to mill the tool post to get it to
hold the tool bits about .045 lower. Mine was sitting so high that when
I tried to turn some steel with the carbide lathe tool bits included with
the machine the bit would not cut the metal at all and it actually wore
a circular indent into the front edge of the carbide piece as I was trying
to figure out what was happening.
On the plus side, it was a breeze to take the tool post base down .045"
with the fly cutter.
Tim
I had the same problem with my tool post. I was a little nervous about
changing the tool post itself so I've been grinding the bottom of my tool
bits. A while ago I saw an ad in harbor freight for some 1/2" shank, indexable
carbide bits. It was a 12 piece set for $26.00. I didn't think I had much
to lose so I ordered some. They work fine and to my suprise, they were
dead on center! I'm glad I didn't change my tool post. Shoptask sells a
set that looks the same. I wonder if they line up. Anyone have the shoptask
set?
Duane
I had the same problem, I had to remove aabout 0.090" on mine. Since
then, I have received my Quick Change Toolholder from shoptask, no problem
with that one as it is adjustable.
John
Regarding the high toolposts, there are some variables, which create
this- the various components of the machine all being on the high side
will cause the post to be high, also we have found that some of the 1/2"
brazed carbides have the tips a bit high etc. Its a tough situation trying
to get the post right on, and then find tools that are off- also those
harbor freight units were a lucky deal, as they were actually 12mm units
labelled as 1/2". We have a sample adjustable toolpost at the factory now,
and will offer as a retrofit once its tested. Thats the only real solution
to the height question. ( figure another 3-4 months)
jt
Floating Dial locks
When I visited Shoptask a couple of weeks ago, I saw a simple machine
modification I thought I'd give a try and then share with the forum.
They had drilled and taped the face of all the english marked floating
dials to accept a small thumb screw. The thumb screw can be tightened to
positively lock the dial in place against it's feed screw.
Now I know you're not supposed to rely on the floating for accurate
measurements, but if you've had the dial slip on you after zeroing it,
it's at least aggravating. The thumb screw lock eliminates any chance of
loosing your zero.
We have a kit with 3 thumbscrews, instructions and a drill and tap -
takes about 45 minutes for the whole job. part is ST 133- price 14.95
jt
A note on start capacitors-
These are the weak link in any capacitor start motor. The reason is
that they are generally rated at a set number of starts per hour- ours
are 20, or one start every 3 minutes. If you are doing a job that requires
more frequent starting and stopping of the motor, let the unit rest for
a few minutes every so often- this will allow the capacitor to rest up
a bit. We are testing a new feature that allows you to stop and lock the
lathe spindle while the motor is running for those type of jobs- The mill
seems to not be a problem as most people leave the motor running longer.
jt
Tailstock
Had my tail stock come apart on me tonight and thought I'd pass it
on. My machine is pre 97 and things might have changed.
While turning the hand crank in the sleeve in front of the crank popped
out the back of the tail stock. I figured the set screw under the crank
was loose so I tapped the whole mess back in and tightened the screw. It
came back out so I decided to take the thing apart and have a look.
The sleeve has an oil journal on top and a small dimple on the bottom
to accept the end of the set screw. Problems:
1. When the sleeve was in place, the dimple was not in far enough to
line up with the set screw.
2. The end of the set screw was too big to fit into the dimple in the
sleeve.
Fix:
The dimple is not drilled in the center of the sleeve so I turned the
sleeve around. Seems to line up better. (Maybe the thing was put on backwards
at the factory). Then I ground the end of the set screw a little to fit
in the dimple.
I put it back together, locked the tail stock down and cranked a live
center against my work to see if I could back the sleeve out. I could not.
Duane
The tailstock design has not changed for quite a while
If you are doing some work that puts a lot of pressure on the tailstock,
we recommend you check the set screw often- you may want to replace it
with an allen type for better grip- ( 6mm X 1 ) Some have drilled a second
hole in from the side and put in a second screw for better grip.
jt