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PM25- Roller Bearings for End Plates of Lead screw?

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alfaspider

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#1
Has anyone added roller bearings to the end plates for the lead screw of the PM25, or similar mills?

Recently added a DIY table motor drive to the left side and removed one end plate. The end plates have oil ports, which I assume are sufficient for hand cranking the table. With added speed/movement from a motor drive there might be excess wear on the lead screw, so wondering if any one has added ball bearings to reduce friction?

Don't anticipate going CNC anytime soon but would like to see if anyone bored out the end plates and what type of bearings might work best for limited home/hobby use. Thanks,
 

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BaronJ

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#2
Hi Alfaspider,

When I made my mill table drive I simply replaced the handwheel on the left side, leaving the end plate and bearings intact.
I replaced the handwheel with a plastic gear and drove that from a car screen wiper motor.
Mill-Table-drive.jpg
 

alfaspider

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#3
Thanks,

But I was asking if you added a roller bearing where the lead screw goes through the end plate of the mill table. Also if anyone added roller ball bearings to the other side of the table for the hand crank.

My DIY motor drive is pretty much the same thing with an aluminum plates and a wiper motor driving some plastic gears.

On the PM25 there is a white removable endplate and an oil port for lubrication. I think a roller ball bearing needs to surround the lead screw to reduce additional friction from the motor drive that is added.
 

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BaronJ

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#4
Hi Alfaspider,

No ! My mill already has ball and thrust bearings in the end plates, on both ends.
 

alfaspider

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#5
OK- thanks-

The PM25 sold here by Precision Mathews does not have bearings or even bushings at either side of the table. It does have oil ports near the hand crank. This mill is sold in other countries, so perhaps different importers set different production requirements?

Can not tell what brand or model you have, but the gear drive looks similar to one I put together using a wiper motor.

CNC conversions usually add roller bearings and a more precise lead screw, but I am just concerned about increased friction and wear of the un-bushed lead screw with using a motor drive. thanks again
 

BaronJ

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#6
Hi Alfaspider,

Sorry ! My mill is an Optimum BF20LB. Each end of the table has a ball race and a thrust bearing. The backlash is taken out by adjusting the nut that holds the handwheel on. I modified the plastic gear with a brass bush that simply replaced the handwheel. The gear is driven by one of a pair of gears that is in turn driven by the gear mounted on the wiper motor shaft.

Table_Gear-a09.JPG Table_Gear-a10.JPG
These pictures show the gear and the brass bush that I made to replace the handwheel.
 

T Bredehoft

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#7
I put ball bearings on each end. I noticed, before I put the motor in it cut the effort by 1/3 to turn the crank.
 

BaronJ

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#8
Hi Guys,

Certainly adding ball races and thrust races to the table leadscrew will improve the feel and can be used to reduce backlash. Actually it surprised me a little that the mill in question only had plain sleeves and no thrust bearings. I would have at least expected those.
 

alfaspider

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#9
Thanks--
Noticed the chip tray was green and not blue..., but not sure if this mill is sold outside the US as a different make, model and /options...

I did pretty much the same thing for the table drive, only used 3 gears: one on the table lead screw, one on the wiper motor arbor, and an idler gear that is used as a clutch.

What is the setup for your directional change lever? Noticed the arrows in your first photo. How does it engage and dis-engage the drive? Can you add a couple of closeup photos?

I made plywood templates for the end of the PM25 table, and positioned some plastic gears on arbors for the motor and table, then a swing arm lever to move the idler gear.


(was working with a friend on similar project so shot short video clips to send back an forth to explain my trial and error progression.


This has worked fairly well, but I may redesign the gear box, add some bushings on the motor arbor and the ildler lever, and then roller bearings on the end of the lead screw.

Thing is it seems to work for now.
 

dcsleep

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#10
My PM-25MV has bearings on the right side but not on the left. There's a bearing on each side of the end flange. Tightening the handwheel nut links the table to the leadscrew and loads the bearings to eliminate any play in the table movement (beside the leadscrew backlash adjustment). This makes the right handwheel the "driving" end of the table. The left handwheel simply turns the leadscrew so it appears the designers felt a simple hole with lubrication was sufficient. All of this is shown in the component diagram in the manual.

I've considered adding a bearing on the left side as well but not sure it's needed so I haven't done it. Interested in what others think.
 
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alfaspider

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#11
Thanks-

When constructing a table motor drive I removed the left side X-support flange ( #33 ) and saw there was no ball bearing, only an oil port.

Someone on this forum had mentioned adding ball bearings to the table lead screw, and I didn't take the right side apart (or notice detail in the parts manual).

I am still wondering if using a motor drive will increase the friction or wear on the left side of the lead screw and will probably try to insert a bearing when re-doing the gear box assembly .. Thanks again for the comment.
 

BaronJ

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#12
Hi Alfaspider,

The knob and lever on mine operate a tumbler gear that causes the table to move left, stop, right. Most wiper motors are only intended to run in one direction. Hence the tumbler.
04072014-02.jpg 12072014-019.jpg 12072014-030.jpg 12062014-01.jpg 16062014-007.jpg
Hope this helps.
 

alfaspider

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#13
Hi Alfaspider,

The knob and lever on mine operate a tumbler gear that causes the table to move left, stop, right. Most wiper motors are only intended to run in one direction. Hence the tumbler.
View attachment 274940 View attachment 274941 View attachment 274942 View attachment 274943 View attachment 274944
Hope this helps.
Thanks- I used a DTDP switch to reverse motor rotation, and have noticed that one direction appears bit smoother than the other. Assumed it might be due to gear orientation, but never thought on differential in motor orientation.

That has not been mentioned in any of the videos I have been able to watch?

Did you machine all of the lever, tumbler and gear housing? or is it some sort of available gearbox such as in a power wheel chair? Thanks
 

BaronJ

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#14
Hi Alfaspider,

I machined everything you see except the plastic gears, and even those were modified as you could see from the brass center. The gears were salvaged from an old Ricoh photo copier.

I don't know if you took the wiper motor gearbox apart, but if you do you will see that it has a thrust bearing at one end of the worm. The motor direction should be such that the bearing takes the load rather than the motor bearings. In addition my motor was a two speed one, the speed change using an offset brush on the motor commutator, this brush effectively moves the armature field round about 25 degrees thus causing the motor to run more slowly.

I powered mine for a while from a variable voltage power supply to get some Idea of current consumption. At 12 volts it only takes about 2 amps. Depending upon what I'm machining 7 volts or there abouts is all that is needed, though I have fed the motor 30 volts to get a quick traverse. The motor doesn't even get more than just warm.

You may have noticed in the very first picture a thick white plastic block. Also just visible in the picture with one white and two black gears. Those two black gears are supported on shafts pressed into the "Nylon 90". The original white gear turned out to be too large, so I machined a second one to mount on the mill table. That nylon block is supported by the collar that contains the shaft bearing and thrust race on the mill table end. It has the rod fastened in it that supports the clutch.
04072014-05.jpg
Here is a view before the alloy support plate was bored out to fit the table.
Load_Current-02.JPG
The load current taken whist driving the table at 12 volts.
Mill_Table_End-01.JPG Mill_Table_End-03.JPG
I'm sure that you don't need any explanation for these last two pictures.

These mills are a German design, and like most are made in China. They are very good mills but need some fettling to get the best out of them.
 

alfaspider

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#15
Thanks, I have not taken the wiper motor gear box apart, and not previously heard of the thrust bearings being only on one side of the gear enclosure.
This is not mentioned in one video that seems to get views here:
Now assume that my speed in different directions may not be just my plastic gear mis-alignment. I did notice the motor housing getting warm with extended use.

Gears I used are a stock item for Briggs/Stratton lawn mower starters, and about $1.25 USD each- (cheaper in bulk) . I epoxy two together to get a grear that is 1" wide, and bore it out to fit onto the motor arbor, or table lead screw.

The photo of left side of your table appears to show a bearing housing which is not on the PM25 sold here. I have a removable end plate that supports the lead screw without bearings ( a, b ). It does not even have bushings, but does have an oil port. The right side of the PM25 table may have bearings ( c ), but I have not taken it apart yet. These are also made in China but to different specifications. Have only had this for month or so, and no previous experience, so appreciate your comments.
 

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BaronJ

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#16
Hi Alfaspider,

I assume that your mill could have either end plate fitted on either end !

If that is the case then I see two options, buy a spare right hand end plate, or make one ! Which is what I would do.
You need to check that the leadscrew is sufficiently long enough to do that first.

At least if you make one and the leadscrew is short, you could move the bearing housing under the table a little.
 

dcsleep

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#17
BaronJ - Interesting design. I like seeing how people come up with different solutions. Can you elaborate a little more on how your clutch mechanism works? From looking at the pictures, I'm guessing that the white nylon block rotates around the bearing housing in the table end cap and engages/disengages the black gears with the motor gear. The table direction depends on which gear is engaged. Is that how it works?
 

BaronJ

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#18
Hi Dcsleep,

Yes you have got it ! The pair of black gears are in mesh but only one of them can drive the table gear at a time. The clutch is a simple dog that ensures that the gears cannot push themselves out of mesh. I learn't that the hard way.

Whilst I remember ! The wiper motors, can be left or right handed even though they both turn in the same direction. Mine came from a motor wreckers, for the time it took to remove them just before the car was dropped into the crusher. Mill_Table_drive-04b.jpg
This is the drawing that I did when trying to work out dimensions. The central gear is the one on the wiper motor spindle.
 

alfaspider

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#19
Hi Alfaspider,

I assume that your mill could have either end plate fitted on either end !

If that is the case then I see two options, buy a spare right hand end plate, or make one ! Which is what I would do.
You need to check that the leadscrew is sufficiently long enough to do that first.

At least if you make one and the leadscrew is short, you could move the bearing housing under the table a little.
----
I have already removed the left hand end plate and installed a DIY motor drive consisting of an 1/2" aluminum plate so will have to bore out the gear box plate and install a roller bearing. I was not aware that the right hand side had bearings. So may try to find something similar. Never took the right hand end plate off, so far..... Thanks for comments. This is first mill, and only have had it for month or so..
 

BaronJ

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#20
Hi Alfaspider,

Ah, you haven't had the table off then ! I stripped mine and cleaned the dovetails. To be honest they are rough to say the least, whilst it is good for oil retention, it does nothing for how smoothly the table travels. Polishing the gib strip helps but it really needs replacing with a brass/bronze one. It only touches at the ends.
 

alfaspider

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#21
Hi Alfaspider,

Ah, you haven't had the table off then ! I stripped mine and cleaned the dovetails. To be honest they are rough to say the least, whilst it is good for oil retention, it does nothing for how smoothly the table travels. Polishing the gib strip helps but it really needs replacing with a brass/bronze one. It only touches at the ends.
--------
is there a supplier or vendor that has the bronze gib strips ? or did you make them yourself. this is first mill, and I have added a few options, but not stripped it down yet.
 

BaronJ

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#22
Hi Alfaspider,

Not as far as I know, there is no one that makes them ! All I did was rub the rough edges off and put everything back. The gibs are tapered ones and look like cast iron. Carefully adjusting things helped though.
 
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