Extracting a dowel pin from a blind hole

[Phil PembertonParticipant @philpemberton74433]

Hi all,

Some of you might have seen my thread about the Hobbymat MD65 over in "Tools and Tooling". I've got a small problem with a metal dowel pin…

There's a yellow support which the front of the carriage rests on. This is held in place with one dowel pin on the left, and two on the right. Sadly it appears the previous owner has managed to drive the pin into the blind hole deep enough that there's nothing to grab onto… this is making the support a bit unstable.

Does anyone have any good tricks for getting these pins out?

Right now my best plan is to turn a small cylindrical drill bushing from a piece of scrap and use that to guide a drill bit into the pin. Hopefully I can then use "something" (possibly a self tapping screw) to pull the pin out.

Thanks,
Phil.

[Phil PembertonParticipant @philpemberton74433]

[John ReeseParticipant @johnreese12848]

True dowel pins are through hardened. Yo will not be able st screw something into it.

Can you drill through the other side of the part so you can get a punch on the pin? If that is not possible set it up on the mill and cut out the pin with a carbide end mil.

[Phil PembertonParticipant @philpemberton74433]

Sadly not. I've drilled into the support bar behind the pin, but I can't get enough leverage to push it out. If I make the hole any larger, it'll compromise the support bar.

The bar is about 50cm long (haven't measured it), 10mm thick and 20mm wide. Knocking a punch in from behind seems impossible.

One other plan I had considered was to drill a hole in behind the pin at a steep angle – I need to have a think about the practicalities of this and how to repair the bar afterwards.

[HopperParticipant @hopper]

Some pics of what you are working on sure would help.

Have you tried heating the "bar" with a propane torch to expand it and then bang it on the bench to shake the dowel out?

You should have a try at drilling the dowel pin. It may not be a through-hardened pin. It may be soft enough to drill and tap to extract. Some pins are case hardened, so you might be able to Dremel the hard case off the end and then drill it. Other pins are just plain mild steel that could be drilled easily. Only one way to find out which you have…

[NimbleParticipant @nimble]

Could you apply a needle point grease gun to the already drilled hole and use the hydraulic pressure to force the pin out. Mechanics use a similar method to drive the spigot bushes out of a fly wheel,alternatively enlarge the through hole to a small pin punch diameter and fill with oil, then drive the pin punch into the through hole refilling with oil when necessary.

Nimble Neil

[JasonBModerator @jasonb]

Looks like part No12 on page 38 of the manual so no way of drilling and punching

[Richard –Participant @richard-3]

Morning,

Try drilling the pin with a cobalt drill, what is the pin diameter?

[David George 1Participant @davidgeorge1]

Hi Phil try pushing some plastercine or similar material down the hole you have drilled behind the dowel then take a punch as near to size of the hole and give it a good thump. The hydraulic pressure should push out the dowel, top up the plastercine as necessary.

David

[Former MemberParticipant @formermember32069]

[This posting has been removed]

[HopperParticipant @hopper]

Posted by JasonB on 28/01/2019 07:43:13:

Looks like part No12 on page 38 of the manual so no way of drilling and punching

Aha. So the dowel is in the end of the long thin bar. Much clearer now.

I think I'd be trying grinding the end off the dowel with a Dremel and trying to drill it out once through the hard skin. Most dowel pins are case hardened, not through hardened, so they retain the strength of the core steel under impact etc. We used to grind the ends off hardened dowels and drill and tap them for later extraction when using them to hold together press tooling, so it can be done if the pin is not through-hardened.

[Howard LewisParticipant @howardlewis46836]

If you can manage to drill a hole through the dowel, as already suggested try using hydraulic pressure to remove it. Hopefully, a pressure oil can will move it out. If this fails, is it large enough in diameter to tap? Probalby too small to screw in a stud, so that a sleeve and nut could then be used to extract it, without stripping the thread. But could you screw in a grease nipple? If so a good grease gun, preferably a side lever, or Wanner type, rather than a pom pom, should be able to apply sufficient pressure to force the dowel out.

Howard

[Martin ConnellyParticipant @martinconnelly55370]

Find someone who can TIG weld a washer edge on to the dowel and pull the washer to remove the dowel.

Martin C

[Neil WyattModerator @neilwyatt]

Count your losses and drill a pair of holes for a new pin?

[egaParticipant @ega]

Posted by Neil Wyatt on 28/01/2019 14:21:44:

Count your losses and drill a pair of holes for a new pin?

Or cut your blessings?

[I.M. OUTAHEREParticipant @i-m-outahere]

Before doing anything I would check to see if the pin is actually hardened by giving the end a rub with a file . You may be lucky and find it is a cheese grade pin ! If it is hardened then cut it out with a carbide end Mill .

[BazyleParticipant @bazyle]

It is not a support bar, just a leadscrew guard of no value to the operation of the machine. Just cut it off and use it to make something else. Replace with a new piece of mild steel that will cost you less than the special drill.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Bazyle on 28/01/2019 15:36:41:

It is not a support bar, just a leadscrew guard of no value to the operation of the machine.

.

Funny you should mention that, Bazyle

I did wonder, earlier today, if folks should be looking at pp 42-43

… but decided to see how the thread progressed.

MichaelG.

[JasonBModerator @jasonb]

Part 12 would seem to fit the given dimensions of 10mm x 20mm x 50cm, note my bold.

Parts 27 on that page and the one before would be the 3 dowel pins that go into the ends of part12

Edited By JasonB on 28/01/2019 19:35:54

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Phil Pemberton on 28/01/2019 02:21:22:

There's a yellow support which the front of the carriage rests on. This is held in place with one dowel pin on the left, and two on the right.

.

Hopefully, Phil will post a photo

MichaelG.

[JasonBModerator @jasonb]

Posted by Michael Gilligan on 28/01/2019 19:37:53:

Posted by Phil Pemberton on 28/01/2019 02:21:22:

There's a yellow support which the front of the carriage rests on. This is held in place with one dowel pin on the left, and two on the right.

.

Hopefully, Phil will post a photo

MichaelG.

Or just look at page 11 of the manual, whether the carrage actually rests on the bar or not I would not like to say but that is part 12. The paint doe snot seem to wear on used ones so maybe it just passes through that slot at the front of the carrage.

 

Edited By JasonB on 28/01/2019 19:51:20

[Michael GilliganParticipant @michaelgilligan61133]

Fair enough, Jason … You win

MichaelG.

.

Edit: Thanks for posting the photo 

… Funny way to design a lathe, methinks.

 

 

Edited By Michael Gilligan on 28/01/2019 19:59:22

[BazyleParticipant @bazyle]

I have a Hobbymat. The bar is non-essential and non-structural.

It is a strange design really being an overgrown watchmakers bar bed lathe. In practice although the bed forms the guide some of the cutting force is taken by the hefty leadscrew which is far thicker than on normal minilathes. I often think it would be nice to rebuild it with only the tailstock on the original bed and a new saddle on say two ground bars.

[Nicholas FarrParticipant @nicholasfarr14254]

Hi, Bazyle is correct and it does not make any contact with the saddle or the tail stock. It's only purpose is to stop swarf dropping straight onto the lead screw.

If I had the same problem, I would lay a washer that has a hole the same size as the dowel, on the end of the bar and then carefully build up the end of the dowel with TIG weld enough to get a pair of grips to pull it out. The washer will help to stop you welding it to the end of the bar.

Regards Nick.

[John HaineParticipant @johnhaine32865]

Maybe the bar is there to help take the longitudinal reaction force of the leadscrew ?

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