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Hobbed Bolt for 3D Printer, how would you make this version?

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roygpa

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#1
I am learning to use my new mini lathe and harbor freight mini milling machine, but 3 D printing is also an interest of mine. Know that I have a lathe and mill, how would you suggest I make a hobbed bolt like the one in this link? the bolt I made with a drmel grinder prior to owning the lathe and mill is slipping and causing me problems.

http://www.ebay.com/itm/Arcols-Hyen...ultDomain_0&hash=item231fb0979b#ht_500wt_1139

Thank you.

Roy

mods: If this is the wrong forum for this question, please move it for me.
 

7HC

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#2
I am learning to use my new mini lathe and harbor freight mini milling machine, but 3 D printing is also an interest of mine. Know that I have a lathe and mill, how would you suggest I make a hobbed bolt like the one in this link?
I don't know but there's a little more information, including a technical drawing here, if you haven't already seen it: http://wiki.arcol.hu/arcol-hu-hyena-announcement

M
 

Tony Wells

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#3
You will need some method of indexing the bolt you make and a cutter of some sort in your mill. It doesn't need to be anything too fancy. A single point ground to the profile you want in the "hobbed" section would be easy to grind. Do you have an indexer or superspacer, or rotary table for your mill? Even if not, there are ways.
 

roygpa

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#4
Do I have "an indexer or superspacer, or rotary table for your mill?" No and no. Not yet anyway. I'll even have to look up what a super spacer is.

I've got some much to learn about machining..
:))

Thanks for the replies guys.

Roy
 

OldMachinist

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#5
You need some way to index the bolt and a cutter with the right diameter and angles. Then it would be just like cutting a gear except you would just plunge the cutter into the side of the bolt to depth, retract, index the bolt and repeat until you've cut all the teeth. You'd need to do some calculations to get the right info on the number of teeth unless you have a sample to go by.
 

OldMachinist

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#6
I guess I was typing when Tony posted.
 

Tony Wells

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OK, photos first.

IMG_5177.JPG IMG_5178.JPG


That is a simple means of indexing a part. That is a plastic gear mounted on a shaft through the aluminum block. It has the proper number of teeth for what I was going to make. I never finished this, but all that it lacking is a pin of some sort to catch between the gear teeth, and a lock for the spindle. The idea was to put this in a vise, at an angle, with a smaller gear blank mounted on the nose, held in place by that cap screw. The shaft fits closely in the block, so it would be relatively precise. It's just one concept you could consider or modify to suit.

IMG_5177.JPG IMG_5178.JPG
 

DMS

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#8
I have used the same method as Tony, and the change gears from mini lathe work great as "index plates". As I recall, the exact form/spacing of the teeth are not that important. They do not technically need to be hobbed. Hobbing (at least used in the method I have seen for producing a "hobbed bolt" for the reprap) will give you slanted teeth like a worm wheel. The method Tony is describing can give you straight or slanted teeth, depending on if you bother rotating the indexing fixture. Either way should be fine. As I recall, the only purpose is to engage the filament to drive it into the extruder nozzle.

If you really want to hob it (and since you don't care about the exact number of teeth), you can use a normal threading tap as a hob. Something like this

[video=youtube;mWVqs_3IfQU]http://www.youtube.com/watch?v=mWVqs_3IfQU[/video]

(your bolt would replace the black delrin blank in the video, and you just need to make a mount to support it.

DMS
 

Hawkeye

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#9
My first thought was to use a tap in a groove roughed out on the lathe with a hand-ground form tool. Then I realized it wasn't a thread you were making. Tony has the elements covered. You already have a set of gears available with your lathe. Make up a block like Tony's stand with the bolt as the axle. If the bolt is larger than the hole in the gears, make it with a smaller threaded section on one end that will clamp the gear and can be cut off when you're finished.

A single-point cutter in what amounts to a boring bar would make your tool when mounted in the mill collet. Tony mentioned a pin to index into the gear teeth and a clamp for the bolt - the plastic gear teeth shouldn't be made to hold the shaft while milling. The clamp is very important.
 
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