Member postings for John Shepherd

Inspired by a picture in todays newspaper, I spent some time browsing the web site of the Vintage Tool Shop at Stalbridge in Dorset.

Very interesting, but I think the value of the contents of my workshop has increased by a factor of X10 if I apply their prices.

John

Ian

It has to be an NVR issue. If there was a fault with the interlock switches etc the motor would (or should not) run when the on button is held down, it would be dangerous otherwise.

Good luck.

Re J Pieczynski Youtube video

Arc sell a micro drill adaptor that works on the same principle.

I think I have saved the cost of it by reducing the number of broken drills

Mick B1 - A question I have wanted to ask for some time. Thanks for raising it.

From the answers given, I think I will base my use of washers as follows:

1. Under the part that rotates
2. To protect a surface
3. If I want to spread the load I will use a large washer not a standard size one
4. It looks right
5. I won't beat myself up if I don't fit one

I saw a chalk drawing on the wall of a factory some years ago that showed a machine screw with legs chasing a nut also with legs and the caption was "not without a washer"

Andy C

I have sent you a PM

I see my 3D printer as another workshop tool. For those that doubt their usefulness, here is a list of some of the things I have made for the workshop:

1. Brackets for DRO on mill
2. Ring light for mill
3. Rotary laser centre finder
4. Lathe QCTP mount for DTI
5. Tool centre height gauge
6. Case for lathe DRO
7. Dremel bench stand
8. Small screw cut to length jig for Dremel
9. Dremel drum sander attachment
10. Rotary Laser centre finder
11. Cases for test equipment
12. Misc knobs and levers

These are in addition to various things for the home and printing parts for my much modified Prusa style printer.

John

Ron

Have you considered using two single pots and connecting the shafts with gears so that one is connected to the control knob and the other is a slave?

The advantages are:

1. you can make mechanical adjustments to reduce the difference (if any) in the two pots.
2. two single linear pots will be easier to source
3. there are plenty of cheap plastic gears around that will do the job.

John

OK moving on from astrophotography and stepper motors, one of the other issues that receives a lot of comment on printers is the standard of wiring and connectors used.

My solution was to move away from the Arduino plus RAMPS controller board that I had used previously and use a Duet3D WiFi board. Not only does this use suitable screw terminal blocks but has Molex KK style connectors that lock in place in one direction only. The board is larger than the RAMPS so that makes room for neater, more reliable, wiring.

I have a lot of admiration for how the RAMPS interfaces with the Arduino but a custom board with several additional features designed for the job, although not without challenges, is a big improvement. Changing over to the Duet was like moving from a ZX81 to a Pentium PC.

The board can be powered by 12 or 24 volts and I decided to opt for 24v. This is a safer option because of the reduced current and the wiring to the heated components can be reduced in size. Consequently, the wiring is easier to terminate and more flexible when it needs to be. Heated beds are normally dual voltage and the cost of replacing the extruder heater and the fans is low. Also, I needed to replace the PSU anyway.

Wiring the print head can be a bit of a challenge with a stepper motor, two fans, a thermistor, and in my case, the IR Z probe. A small PCB and removable multiway connectors made wiring much neater and maintenance easier. The heater uses a separate ‘Deans’ connector often used as a battery connector on model cars etc. though.

Good quality crimping tools made for the connector in use are a must and I have learned the hard way by skimping on these. Some people recommend soldering crimps, but I believe there are good reasons not to do this and prefer to use them as intended, besides if crimp connections are good enough on aircraft, they are good enough for my printer.

Has anyone got any alternative solutions?

John

Picking up points about the Z axis that MAY make a difference for better or worse.

First re Steps/mm – my M92 Reprap Gcode values are X80 X80 Z400 E417 ; set steps per mm. using an Acme 4 start lead screw

I have seen a lot of comment about fitting bearings on the free end of the lead screws and as I have not experienced much in the way of wobble have followed the example used on my lathe cross slide and other x y tables where the free end is left to float. Perhaps someone could explain the pros and cons of this?

I used a plum connector to connect the leadscrew to the stepper motor, not particularly because it provided better alignment, in fact the axial movement is quite stiff, so I doubt it moves much with the loads applied to it, but because it has a clamping arrangement on the two shafts. My previous coupler was just a straight one held in place with grub screws. I didn’t like the idea of grub screws on shafts with no flats or indentations because of the possible damage that might make disassembly and reassembly difficult. I also tried the flexible couplings with spiral slots in them, but these introduced more wobble and artefacts on the vertical part of prints, probably due to poor manufacture or perhaps design. Again it would be good to have a definitive view on the use of these.

In the past I have tried the sprung anti backlash nuts on the lead screws and these were useless, in any event the weight of the carriage on the Prusa takes care of that. I now use Delrin nuts that are smooth and don’t have much play.

John

As promised, here is my printer:

Ok Here goes.

I will feed in just one or two mods/issues at a time to hopefully keep the thread focused.

My printer is based on a Prusa i3 and uses a Duet WiFi board (perhaps more on that later). It runs on 24v, has a laser bed level compensation system, heated bed and a glass print surface. ( I will add an image later)

The issue that raised some response was using an Acme leadscrew (or a ball screw) instead of threaded rod as used on the Z axis in the original Prusa design. It was suggested that using a Ball screw (and I suppose an Acme thread), threw away resolution. My printer came with Acme threads on so can’t comment on if there is any improvement in print quality but it seems to make sense to use properly machined components made for the job rather than studding that because of how it is made may not be straight or have a great deal of dimensional accuracy.

At the risk of getting the math wrong, I won’t go into the calculations, but my z axis parameter is 400 full steps for 1mm movement. The TMC 2660 driver on the Duet has 256 micro stepping and I can get Z movements of 0.05mm with repeatability by using the function on the interface. I don’t think that is any sort of compromise. Smaller value ‘Baby step’ offsets can also be made on the fly and can be useful in making adjustments to squash down a first layer on difficult prints, it is also useful for setting up the nozzle height above the board, but I have not found any other uses for it.

Connected with the Z axis is the laser module that is used at the start of each print to adjust one of the two Z axis motors to eliminate any tilt of the bed and then to measure the relative height of each corner of the bed so that software corrections can be applied if needed. It also acts as an ‘endstop’ and allows precise setting of the nozzle to bed height.

That all for now, but there is more!

Following on from an exchange of views I had with Neil in another thread about how many of the popular 3D printers are engineered, is there any interest in a new thread about the subject?

In a thread about cheap printers, I complained about what I consider to be poor practice such as bearings held in place with cable ties, poor rigidity, 'all threaded' rod used for construction and for lead screws etc. and outlined some of the modifications I have made.

Neil expressed the view that the loads and demands on a 3D printer are a lot less than on machine tools and there is no need to employ the same engineering standards.

My stance is that there are many variables in 3D printing and it is good practice to reduce as many as possible. Besides, I am more at ease using a better engineered printer just as I would be when using any other well made machine.

I realise that a lot of printers are supplied as kits and many users do not have engineering experience to build a complex design or the machining facilities to improve them, but if that route gets them into 3D printing that is good.

There are a lot of modifications to 3D printers featured on the internet and many of them are ill founded, so perhaps it would be good to get some input from the wealth of knowledge on this forum?

If there is an appetite for it, I will be happy to put my head above the parapet and put my thoughts on the firing line.

John

Neil

I take your point about some of my mods not making much difference but take issue on the 'mistake of replacing threaded rod with ball screws' . A machined ball screw can provide greater precision and at least equal resolution as long as you also upgrade the stepper driver.

There are many variable when 3d printing and I think it is good practice to reduce as many as you can for piece of mind if nothing else!

John

I was grateful to receive a Prusa 3D printer from my Son when he moved onto another design.

It performed ok but what annoyed me was the poor engineering :

1. Threaded rod and plastic parts to form the base for the bed.

2. Linear bearings held in place with cable ties (later models used U bolts on the bed bearings but that was not much better IMO.

3. Printing surface mounted on springs so that it could be adjusted to make it level. I accept that levelling adjustment is needed, particularly as the bed base plate cannot be relied on to be flat, but this introduces instability and side to side movement.

4. Stepper motors coupled to Acme lead screws with simple joints using grub screws (no flats on either as well).

5. The vertical frame was not braced in the original design.

6. The bed runs on 8mm dia rails that can only be supported at each end. This is not as rigid as it could be.

I accept that some of these issues have been addressed in later models but my mods so far include:

1. New base using 30 x 30 extrusion and aluminium end plates for the base.

2. Replaced all linear bearings with ones enclosed in housings that have mounting holes and made an aluminium X carriage to replace the plastic one.

3. Printing surface mounted with silicone spacers to give some adjustment, but with much reduced side to side movement.

4. Used Flexible Plum Couplings with a clamping action rather than grub screws to connect stepper motors to lead screws.

5. Braced the frame using aluminium supports.

6. I am about to replace the round rods and bearings on the bed with flat linear rails that can be supported along their entire length.

There are several other minor mods including those to wiring, belt fixings and tension adjustment etc. and I do get prints I am satisfied with.

I suppose my point is that a cheap printer is just a kit of parts as a base for development, like some of the cheaper Chinese machine tools judging by the number of modifications that appear in MEW etc.

John

Oh dear! A perfectly reasonable opening post and we drift on to debates about rotten fish and tightening chucks.

Now that has made my mind up about not contributing in future.

Mark C

I am sorry I don't understand what you mean by 'fast'.

Am i right in thinking you mean 'fact' (not being pedantic just need to make sure). If so, yes I agree.

Edited By John Shepherd on 24/01/2017 18:10:38

Thank SOD for raising this, I share your concerns.

Another thing that annoys me is when there is a post asking for advice on a particular subject or machine and they get a reply such as "I know nothing about it/ don't have such a machine, but..." and what usually follows is of no use at all.

1. Expecting moderators to take action, unless there is hostility or obvious bad practice, can be difficult for the moderators and can escalate the problem if my experience of other forums is to go by.

2. Unless I am sure of my facts or have recent experience, I would rather sit back than offer an opinion. Many things I did in my early career are now looked on as bad practice and I would rather learn from that than say 'we always did it that way and no harm resulted from it'.

3. Why must people get on the bandwagon as soon as Health and Safety is mentioned? Most of the time we are not concerned with not playing conkers, just helping with good practice so that many of us can continue with our hobby with our hands and eyes intact.

4. A recent thread on Consumer Units was a good example of some misguided information. A good case if there was one of understanding the subject before replying and a need to point to some independent up to date evidence and regulations.

So

5. If you don't agree with a post or the advice it offers, perhaps it is best to explain why and offer evidence rather than wading in with an opinion or comments like ' in all my years as a professional xyz we never did it that way'.

6. Humour can be a good let out but often it is misread, so use it carefully, especially if it is directed at an individual.

7. From John Reese: 'There are those who hold strong opinions that are not based on fact or experience. In that case, the best approach is silence.' This is the stance I usually take and it results in non-contribution rather than taking part, but if we had a more open forum it would be better for everyone.

8. I have been close to canceling my subscription to this forum because of some of the comments, so please can we all realise what is wrong and make sure that the tremendous amount of good information is not diluted and make it a happier place to visit.

John Shepherd.

Daniel

Have you actually checked the threads to see if they are R or L handed?

Another reason for the instructions stating that a grinding wheel should not be fitted is perhaps the lack of large dished washers. The brush mounting may not need these because of its metal hub but the grinding wheel needs them to spread the load.

Went to the Haynes motor museum a few years ago and they had a special Ferrari exhibition. There was a document on display that showed the permitted sizes and proportions of the logo for a variety of uses, the tolerances were very tight as I recall.