I need a part made

1162 Views 60 Replies 10 Participants Last post by JayArr, 14 d ago

JayArr

Discussion Starter · 4 mo ago

Hi All

I was directed here from the woodworking forum and it was suggested I see if anyone wants a project.

I want a plastic piece made for a Craftsman Radial Arm Saw. You can see a picture of it attached. It's about 3.5" x 3.5" x 1.25" tall.

It was made of thin, brittle plastic and it broke on almost every saw I've ever seen. I was lucky enough to get this sample off a saw, it was already cracked and broke apart as I was removing it but I saved all the pieces and glued it back together.

Since it's symmetrical I'm hoping that one half can be scanned and then mirrored in the software to create a full, unblemished, image. I'd like at least three made, I could poll over at Woodworker Talk to see how many more could be required. The maker could then sell them on eBay or etsy etc.

I'd like the new ones to be made of a thicker more durable plastic, they will get a lot of vibration since they are on the side of a saw motor. I'm willing to mail my sample to someone who wants the gig.

If this is the wrong forum I hope that the mods will move it to the correct one.

JayArr

Rectangle Wood Gas Circle Gadget

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Oscar56

· #21 · 3 mo ago

I model in standard and have to convert to metric for 3d printing. CURA does not have the option to work in standard. Have to multiply everything by 2540%.

My cnc software has the option to work with either metric or standard.

The CAD software I've used can use either metric or standard.

This model should be easy to do in any CAD software. I don't use CAD so only speculating.

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MadMark

· #22 · 3 mo ago

You can 3d print that part, but that part isn't designed for 3d printing. Specifically, the mounting tabs will snap off if the piece is printed flat. To get any strength at all, it will have to be printed on edge.

In reality, this piece is just a dust cover, the tool can likely be safely operated without it, albeit possibly with reduced bearing lifetime.

RT3360

· #23 · 2 mo ago (Edited)

I’ll take a shot at modeling it this week. If I get it close, I may need additional dimensions, but first I’ll try making a drawing to include the dimensions and send that to you to verify. Then I could see if my friend could print it out of TPU. I may also try to add some things that might keep it from breaking. The sharp corners at the mounting tabs are definite stress points where cracks would start. The TPU being very flexible should also help. I’ll let you know how it goes.

By the way, I am retired and sometimes I need things to keep my skills sharp. I was an electronics design engineer that also enjoyed pc board design. Since working with 3D CAD, I’ve gravitated back to it and using it to make things in metal, wood, printed plastic.

We’ll see how this goes and maybe I’ll be able to help you with other things.

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RT3360

· #24 · 2 mo ago (Edited)

JayArr said:
Hi John Smith

I've worked with casting as well but only at a hobbyist level, Smooth-Cast was the product name. It's a lot of work, the chemicals can be expensive and they have a shelf life and the result can be less than perfect. I like the idea of having a file on a computer as opposed to a cast on a shelf, the casts wear out but the file never will. It also seems that although the printer may take a while it's pretty much unsupervised. A maker can tell it to make a part and go to bed and in the morning there are finished parts waiting at the machines. I think that's terribly efficient. I thought this was the kind of small gig that a maker could use to fill in gaps when his printer isn't doing anything else. It's also not too critical so a maker just starting out could practice with it and still make some $$.

If I wasn't so close to retirement I'd buy a printer for my business. being able to fabricate parts would go hand in hand with repairing electronics, we're always glueing plastic back together and fabricating small parts.

Hi John Carlisle

The current thickness is 1/16" which would be totally fine if the plastic didn't crack and fall apart. It's just a cover, it takes no load or stress other than vibrating with the motor as the saw cuts. It's purpose is simply to cover a rotating part so the operator doesn't accidentally hurt themselves by touching it.

Maybe the problem isn't the thickness, maybe the quality of plastic in the 70s and 80s just wasn't good enough to hold up. If the material was stronger, then I think 1/16" would be fine, if the material stays the same strength, then I think it should be 1/8" get the idea?

I'll take some pictures today with a ruler and some measurements as well as how it mounts on the saw.

Found it a little challenging to get it close, but here's what I got.

I couldn't read some of the dimensions due to the glare of the light on the scale, so I took an educated guess.
Please mark up attached drawing and I'll make appropriate changes. Then I'll see how best to strengthen the walls a little so I can use TPU, but still have a rigid part.
I did increase the mounting tab thickness to 1/8" and added some fillets.
Wall thickness is currently set to .080".
Mounting hole note says 90 degrees, but should say 180 degrees.

It would definitely be easier to have the part in hand to model the part correctly. Let me know what you think.

EDIT:
Went back and changed dimensions to across the body side-to-side and top-to-bottom to be the same. It squared up just fine.
Now I just need confirmed dimensions:

top to bottom outside (3.68")
side to side outside (probably should be 3.68")
width of mounting tab (1" before radius added)
width of flat on each side (2.625" [2 5/8"] before radius added)
approximate radius of corners (estimated .25")
Diameter of large hole (1")
tab (extends .438" [7/16"] from body and matches the flat width)
mounting hole diameter (.19" for #10 screw)
location of mounting holes in tab (.188" [3/16"] from end [large side] and side [short side])
tab corner radius (.125")
tab thickness (wall thickness [.080"] + .0625" [1/16"] )
wall thickness is currently set to .080"

I expect to add some ribs on the outside for stiffening.

around the base, outside
across the top vertical and horizontal, outside the hole
around the hole outside

Bob

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RT3360

· #25 · 2 mo ago (Edited)

Had another thought about the cover.

The critical dimensions are the inside of the cover where it mates to the metal and the height to clear the magnetic clutch or motor parts. I used external dimensions, but increased the wall thickness slightly which could create an interference. Better dimensions with a set of calipers would be most valuable.

This is a great example of how critical dimensions are determined when designing mating parts like this cover.

Hope we get some info from the OP. I don’t know how else to contact him. I can’t proceed with making a part without clear direction.

JayArr

Discussion Starter · #26 · 2 mo ago

I'm back, got busy at work and wasn't paying attention.

I can take the caliper to it but if you like I can also mail you the part. It may take a few days to get to you but then you can really see it for yourself.

I think there's lots of room under it. The one I have has two cracks that both started at the corner of the tab and worked their way inward. Fillets in those corners would likely help a lot.

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JayArr

Discussion Starter · #27 · 2 mo ago

I took my vernier to it. Some of the dimensions are hard to get exact because you're measuring from a corner radius but I think this should be pretty accurate. I think if we reduce the amounts to nice even numbers we'll be fine. Eg: 0.76 is 3/4", 3.385 = 3 3/8", 2.77 = 2 3/4" etc.

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RT3360

· #28 · 2 mo ago

Here's the revised (rev2) drawing.

I got the housing corners as close as I could to what you provided. With radii on all the corners, it's tough to get the actual dimensions. Housing corner dimensions are driven by the width of the side where the tabs are and the width of the two sides.
I added stiffeners around the base to the outside and on top around the hole plus fillets.
The tabs are thicker to withstand the pressure the screw will put on the tab.
Wall thickness is .08".
I added fillets at the corners of the tabs to reduce the chance of cracking.

Dimensions used were:

Width and Height (outside) - 3.385" - Changed CHECK
Height - 0.765" - Changed CHECK Not including the stiffening ribs on top.
Tab Width - 0.760" - Changed CHECK
Tab Height - 0.457" - Changed CHECK
Tab Fillet Radii (added to reduce stress cracking) - 0.080" - BEST GUESS
Tab Thickness (added to reduce cracking) - 0.143 (0.080 + .063") - BEST GUESS
Tab Corner Radii - 0.125" - BEST GUESS
Mounting Hole diameter - 0.175" - Changed CHECK
Mounting Hole from base - 0.250" - NEEDS VERIFIED
Mounting Hole from side of Tab - 0.207" - NEEDS VERIFIED
Mid Side Height - 0.455" - BASED ON MAKING THE CHAMFER 1/2 THE OVERALL HEIGHT.
Outer Radii - 0.250" - BEST GUESS
Wall thickness - 0.080" - BEST GUESS
Other Fillet Radii - 0.065" - BEST GUESS

Looking forward to getting the housing to double check. Hope this gets us pretty close on the first try.

Bob

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Oscar56

· #29 · 2 mo ago

schematic looking sharp!

RT3360

· #30 · 2 mo ago (Edited)

After studying photos of the installation more, I realized the critical dimensions were the inner dimensions.

I found a shell command can be inward or outward, so I modeled the interior of the cover, added detail, then shelled the material outward. That would allow changes in wall thickness without losing critical interior dimensions. Then I added one mounting tab and made a two part circular array to get the second one identical.

Had an issue with the first print because I forgot 3D printed parts don’t like 45 angles. Changed to 30 degree and parts printed fine.

Automotive tire Hood Black Wood Computer keyboard

Parts shipping to Jeff for trial today.

If parts need rigidity, I’ve found adding structure to a TPU printed part can turn a flexible part into a pretty rigid part. The material is flexible, but doesn’t compress (or that’s what it appears). It’s a very universal material as far as I can tell.

Definitely helped having the part in hand to measure with a set of calipers.

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JayArr

Discussion Starter · #31 · 1 mo ago

Looking forward to trying it out. Remember it is just a dust cover so rigidity may not be a problem at all. It keeps sawdust out of the brake clutch that is under it and it keeps fingers and clothing from getting caught in the rotating parts.

I agree the inside dimensions are more important, there is a ridge around the aluminum casting that the part fits in.

JayArr

Discussion Starter · #32 · 1 mo ago

Tool Wood Ruler Tape measure Office ruler

Not tall enough. It hits the brake before the tabs get close to the holes.

Take a look at the pics.

Hand Finger Automotive mirror Automotive tire Fender

Trigger Bumper Air gun Automotive tire Thumb

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RT3360

· #33 · 1 mo ago

Increase the height by 1/4” or 3/8”? I remember you said it can’t be too tall.

Can you cut one in half (one side of the mounting tab across to the tab on the other side)? It might shed some light on what is hitting. The only difference is the ribs on the inside, but they are only 0.080” deep.

Sorry I didn’t get it right first time.

RT3360

· #34 · 1 mo ago

RT3360 said:
Increase the height by 1/4” or 3/8”? I remember you said it can’t be too tall.

Can you cut one in half (one side of the mounting tab across to the tab on the other side)? It might shed some light on what is hitting. The only difference is the ribs on the inside, but they are only 0.080” deep.

Sorry I didn’t get it right first time.

Never mind on this reply. Some how I definitely made the height wrong and have corrected it and having new parts made. I’ll let you know when they ship.

My apologies,
Bob

JayArr

Discussion Starter · #35 · 1 mo ago

No worries, it would be against the odds to get it spot on in the first try.

It's too short, I can see it.

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JayArr

Discussion Starter · #36 · 1 mo ago

You may have to play with the contrast on those photos, it's hard to get enough flash to see the black cover without fasding out the ruler.

Could have something gone wrong with the dimensions when you changed it from 45 degrees to 30 degrees?

The material is great, flexible is actually good and it seems thick enough and solid enough.

I like the criss cross pattern the machine makes, it's almost like carbon fibre.

RT3360

· #37 · 1 mo ago

JayArr said:
You may have to play with the contrast on those photos, it's hard to get enough flash to see the black cover without fasding out the ruler.

Could have something gone wrong with the dimensions when you changed it from 45 degrees to 30 degrees?

The material is great, flexible is actually good and it seems thick enough and solid enough.

I like the criss cross pattern the machine makes, it's almost like carbon fibre.

I’m not sure what I did. It happened when I changed the model from outside dimensions to inside. It looks like I used the straight (bottom) dimension for the overall height. As soon as I put one next to the original, I had that sinking feeling. The height to the inside was modeled at 0.495 instead of the 0.820 that it should have been. Parts are being made.again. I’ll let you know when they are shipped.

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A Guy In Town

· #38 · 1 mo ago (Edited)

I would fine a qualified person who can receive that part in the mail, 3D scan it, redesign it to be bigger, better, stronger, have six copies 3D printed, and sell the other five to recover your costs.

Joe

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RT3360

· #39 · 1 mo ago (Edited)

A Guy In Town said:
I would fine a qualified person who can receive hat part in the mail, 3D scan it, redesign it to be bigger, better, stronger, have six copies 3D printed, and sell the other five to recover your costs.

Joe

So are you saying I’m not qualified?

😲 I’m shocked. I made the first model right, but in the process of changing the model technique to make it easier to switch to thicker/stiffer, I made a mistake. Then I didn’t take the first part and set it side to side with the original and had the printed parts shipped. So yes I made a mistake, followed by poor judgement in an effort to get it delivered quicker, but I’m an old retired engineer that takes more tries than it used to. Sorry

Scanning

Scanning just gives you a duplicate of what you had which was made for a specific process (injection molded). I don’t think the OP wanted a duplicate.

Redesign it to be bigger, better, stronger

All of those things are a matter of opinion and how much bigger, better, stronger is NEEDED is always up for debate. Do you want to pay for a VW bug, a Chevrolet, a Cadillac, or a Rolls Royce? All get people from place to place, some in more comfort, and some in style. Which category do you think a saw cover is in NEED of?

Edit: I apologize. I reacted. I know I made mistakes, but have set out to provide good parts to someone I hope to make a friend, usable by him and acceptable parts for the use. I didn’t ask the OP to pay for my mistake, nor do I expect my friend who printed the parts to pay either by not getting paid for his effort. I expect the next parts to work just fine and trust the delay will not be an inconvenience.

It’s my effort at integrity. Have a great day.

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A Guy In Town

· #40 · 1 mo ago

RT3360 said:
So are you saying I’m not qualified?

My reply was to the original post, and not to any response that followed. If the original part broke, and several of them have broken, then the part is obviously designed wrong from the factory, so it would behoove the OP to design something bigger, better, stronger. I did not read through the entire thread, so I did not read anything you may have posted about offering a solution, or having MADE a solution, etc.

Joe

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